Remove dependency on uuidgen

[simondeziel]

ovs-ctl uses uuidgen only on the first startup when there is no system-id.conf file. After the first startup, the freshly created UUID is saved into that file for later use.

By generating the exact same kind and format of UUID ahead of time using systemd-id128 (readily available from core base), we can remove that dependency on uuidgen.

[tomponline]

What project were you working on to come across this out of interest?

[simondeziel]

What project were you working on to come across this out of interest?

Saw that uuid-runtime package while working on canonical/lxd#14497 and that jogged my memory about wanting to drop that snap dep :)

[simondeziel]

This was tested successfully to generate and persist a UUID between snap restarts after doing snap set lxd openvswitch.builtin=true. The patched daemon.start was bind mount for the test and /bin/false was bind mount on top of /snap/lxd/curent/bin/uuidgen to make sure that binary wasn't used.