Use re2 compatible regexes in branch matchers

Python regexes are deprecated in Zuul, so update the use of regexes
in branch matchers with re2-compatible syntax.
The commit also removes matches for branches that are EOL - all
branches until stable/rocky (including).

Change-Id: I461f00415d67ba5af8ad2387fc2d5dd224a733db
3 files changed