switch to re.match to only match at beginning of string
switch to re.match to only match at beginning of string

we were having a problem where rel jobs were created from the
rel-template on branches like "dev-_rel-4.29-blah-blah"

rather than using "^rel-.*" instead of "rel-.*" as our regex, we
switched to re.match which explicitly will only match from the
beginning of the string (which is what we want in our matchers here) and
is also reputedly faster than re.search which we used before

see this explanation:

http://stackoverflow.com/questions/180986/what-is-the-difference-between-pythons-re-search-and-re-match

and from the doc:

Python offers two different primitive operations based on regular expressions: match checks for a match only at the beginning of the string, while search checks for a match anywhere in the string (this is what Perl does by default).

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