capi: ubuntu-1804: use python3

[jsen-]

make build-qemu-ubuntu-1804 was failing on ansible with /bin/sh: 1: /usr/bin/python, adding the python package to preseed.cfg seems to help

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[jsen-]

/assign @ncdc

[detiber]

/lgtm

[ncdc]

@codenrhoden any concerns here?

[hidekazuna]

You may use python2. Please use python3.
https://docs.ansible.com/ansible/latest/reference_appendices/python_3_support.html

[jsen-]

according to comment from @hidekazuna, PR was updated so that python3 is used instead of installing python2

/assign @detiber

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In response to this:

according to comment from @hidekazuna, PR was updated so that python3 is used instead of installing python2

/assign @detibe

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[codenrhoden]

/lgtm
/approve

@codenrhoden any concerns here?

No concerns with this change specifically. On a broader scope, I've always had a bit of unease in that there isn't a clear cutline for different OS's on which ones are only Python2 or Python3. Looking at the Ubuntu DEBs we install, it appears to be only Python3 packages, but the CentOS and Photon RPMs have a mix of 2/3, and I'm not sure if that's really required, or if it's been bandage on top of bandage to keep things working.

So there's some tech debt there. :)

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This pull-request has been approved by: codenrhoden, jsen-

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