git-version-gen: Take into account tags not in master

Latest tag 0.3.0 was created in a release branch instead of master. As a
result, git describe doesn't show them. Let's instead reuse git command used in
osmo-ci to get latest tag from tag list when OBS latest repository is
built.

Change-Id: I3e461d4270b5e6d4c42126df4deef5651dca1e27

git-version-gen

@@ -93,8 +93,7 @@ if test -n "$v"
 then
     : # use $v
 elif
-       v=`git describe --abbrev=4 --match='v*' HEAD 2>/dev/null \
-	  || git describe --abbrev=4 HEAD 2>/dev/null` \
+       v=`git tag -l --sort=v:refname | grep "^[0-9]*.[0-9]*.[0-9]*$" | tail -n 1 2>/dev/null` \
     && case $v in
 	 [0-9]*) ;;
 	 v[0-9]*) ;;