[8.0] Snap update to 18.04 base

[mwinter-osr]

Old snap base (on Ubuntu 16.04) is no longer supported and snap package can't be built anymore because of it.
This updates the core for the snap to be based on 18.04 which is the current recommended version.

Additionally, adds the pathd to the daemons used by snap package

[polychaeta]

Thanks for your contribution to FRR!

• One of your commits has a missing or badly formatted Signed-off-by line; we can't accept your contribution until all of your commits have one
• One of your commits does not have a blank line between the summary and body; this will break git log --oneline

If you are a new contributor to FRR, please see our contributing guidelines.

After making changes, you do not need to create a new PR. You should perform an amend or interactive rebase followed by a force push.

blocking comments addressed

[LabN-CI]

💚 Basic BGPD CI results: SUCCESS, 0 tests failed

Results table

_	_
Result	SUCCESS git merge/9430 4405435
Date	08/17/2021
Start	18:27:03
Finish	18:53:16
Run-Time	26:13
Total	1813
Pass	1813
Fail	0
Valgrind-Errors	0
Valgrind-Loss	0
Details	vncregress-2021-08-17-18:27:03.txt
Log	autoscript-2021-08-17-18:28:13.log.bz2
Memory	493 486 417

For details, please contact louberger

[NetDEF-CI]

Continuous Integration Result: SUCCESSFUL

Continuous Integration Result: SUCCESSFUL

Congratulations, this patch passed basic tests

Tested-by: NetDEF / OpenSourceRouting.org CI System

CI System Testrun URL: https://ci1.netdef.org/browse/FRR-FRRPULLREQ-21147/

This is a comment from an automated CI system.
For questions and feedback in regards to this CI system, please feel free to email
Martin Winter - mwinter (at) opensourcerouting.org.

[NetDEF-CI]

Continuous Integration Result: SUCCESSFUL

Continuous Integration Result: SUCCESSFUL

Congratulations, this patch passed basic tests

Tested-by: NetDEF / OpenSourceRouting.org CI System

CI System Testrun URL: https://ci1.netdef.org/browse/FRR-FRRPULLREQ-21146/

This is a comment from an automated CI system.
For questions and feedback in regards to this CI system, please feel free to email
Martin Winter - mwinter (at) opensourcerouting.org.

[idryzhov]

I tried to build the snap on my system and found a missing libprotobuf-c-dev dependency.
It is fixed and now everything works fine.
CI doesn't check snaps anyway, so won't wait until it finishes.

[NetDEF-CI]

Continuous Integration Result: FAILED

See below for issues.
CI System Testrun URL: https://ci1.netdef.org/browse/FRR-FRRPULLREQ-21187/

This is a comment from an automated CI system.
For questions and feedback in regards to this CI system, please feel free to email
Martin Winter - mwinter (at) opensourcerouting.org.

Get source / Pull Request: Successful

Building Stage: Successful

Basic Tests: Failed

Topotests Ubuntu 18.04 arm8 part 4: Failed (click for details)

Topotests Ubuntu 18.04 arm8 part 4: No useful log found

Successful on other platforms/tests

• IPv4 protocols on Ubuntu 18.04
• Topotests Ubuntu 18.04 arm8 part 6
• Addresssanitizer topotests part 8
• Topotests Ubuntu 18.04 arm8 part 1
• Topotests debian 10 amd64 part 3
• Addresssanitizer topotests part 6
• Topotests debian 10 amd64 part 2
• Addresssanitizer topotests part 3
• Ubuntu 16.04 deb pkg check
• Topotests debian 10 amd64 part 7
• Topotests Ubuntu 18.04 i386 part 6
• Topotests debian 10 amd64 part 8
• Topotests Ubuntu 18.04 amd64 part 5
• Topotests Ubuntu 18.04 i386 part 1
• Topotests Ubuntu 18.04 arm8 part 8
• Debian 9 deb pkg check
• IPv4 ldp protocol on Ubuntu 18.04
• Topotests debian 10 amd64 part 1
• Topotests Ubuntu 18.04 arm8 part 7
• Topotests Ubuntu 18.04 arm8 part 2
• Topotests debian 10 amd64 part 9
• Ubuntu 20.04 deb pkg check
• Topotests Ubuntu 18.04 i386 part 0
• Topotests Ubuntu 18.04 i386 part 5
• Topotests Ubuntu 18.04 arm8 part 9
• Debian 10 deb pkg check
• Topotests Ubuntu 18.04 amd64 part 8
• Addresssanitizer topotests part 2
• Topotests Ubuntu 18.04 i386 part 8
• Topotests debian 10 amd64 part 5
• Fedora 29 rpm pkg check
• Topotests debian 10 amd64 part 0
• Topotests Ubuntu 18.04 i386 part 3
• Addresssanitizer topotests part 9
• Topotests Ubuntu 18.04 amd64 part 9
• Addresssanitizer topotests part 7
• Topotests Ubuntu 18.04 amd64 part 7
• Topotests Ubuntu 18.04 arm8 part 0
• Topotests Ubuntu 18.04 amd64 part 6
• Topotests Ubuntu 18.04 arm8 part 5
• Topotests debian 10 amd64 part 4
• Topotests Ubuntu 18.04 i386 part 7
• Topotests Ubuntu 18.04 i386 part 2
• Addresssanitizer topotests part 0
• Topotests debian 10 amd64 part 6
• Addresssanitizer topotests part 5
• Addresssanitizer topotests part 4
• Static analyzer (clang)
• Topotests Ubuntu 18.04 amd64 part 0
• Ubuntu 18.04 deb pkg check
• Topotests Ubuntu 18.04 amd64 part 1
• Topotests Ubuntu 18.04 amd64 part 4
• IPv6 protocols on Ubuntu 18.04
• Topotests Ubuntu 18.04 amd64 part 2
• Addresssanitizer topotests part 1
• CentOS 7 rpm pkg check
• Topotests Ubuntu 18.04 i386 part 4
• Topotests Ubuntu 18.04 amd64 part 3
• Topotests Ubuntu 18.04 arm8 part 3
• Topotests Ubuntu 18.04 i386 part 9