jenkins-common: Treat -asan builds the same as -master
This fixes the jenkins test failures seen in ttcn3-stp-test-asan. TTCN3 tries to connect to stp via TCP, but since the jenkins.sh script doesn't consider this a build from master the corresponding config is not added to osmo-stp.cfg.
Also change the function names from image_suffix_is_* to osmo_repo_is_* to better reflect what they are doing (instead of how).
