oeqa/utils/gitarchive: fix tag computation when creating archive

oeqa/utils/gitarchive: fix tag computation when creating archive

Sporadic errors have been observed in autobuilder when trying to store new
tests results:

error: failed to push some refs to 'push.yoctoproject.org:yocto-testresults'
hint: Updates were rejected because the tag already exists in the remote.

The new tag name is generated by gitarchive based on known tags from the
repository (learnt with git tag). In autobuilder case, this repository is a
shallow clone, so git tag only returns most recent tags, which mean we
could miss some older tags which exist in remote but not locally. In this
case, gitarchive will likely create a tag which already exists in remote,
and so will fail to push

Fix this tag duplication by using git ls-remote to learn about existing
tags instead of git tag. To do so, create a helper ("get_tags") which
manages both nominal case (target directory is a git repository with a
proper remote) and fallback case (target directory is not from a clone, no
remote has been configured)

Fixes [YOCTO #15140]

Signed-off-by: Alexis Lothoré <alexis.lothore@bootlin.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>