read-version: When insufficient tags, use cloudinit.version.get_version

[blackboxsw]

Proposed Commit Message

read-version: When insufficient tags, use cloudinit.version.get_version

Additional Context

Test Steps

git clone --no-single-branch --depth 50 https://github.com/canonical/cloud-init.git
cd cloud-init
git fetch origin --force --tags --prune --prune-tags --depth 50 pull/1879/head:external-1879
git checkout --force ac0795a9ff76c48ca74ae23b5766543ef6785387
git apply <this patch>
./tools/read-version

Checklist:

• My code follows the process laid out in the documentation
• I have updated or added any unit tests accordingly
• I have updated or added any documentation accordingly

[TheRealFalcon]

Can we instead use what's defined in version.py?

[blackboxsw]

Can we instead use what's defined in version.py?

I think that'll work too. Our only goal with this is to make tools/read-version more resilient in the face of a missing annotated tag.
I've updated the PR