use re.search to filter tests in --run

re.match only find matches where the pattern appears at the beginning of
the string, whereas re.search matches if the pattern appears anywhere in
the string. This is behavior is consistent with pytest, go test and ERP5's
runUnitTest

For more details, see the discussion from nexedi/nxdtest!6 (comment 121409)

/reviewed-on: nexedi/nxdtest!8