git-ls-remote accepts paramter refs to just return refs for specific
ones. This refactor uses this parameter to avoid handling full list of
refs from remote repository.
In original code, option --exit-code is passed to git-ls-remote, which
would cause command return exit code 2 when no ref is found from remote
repository. SCM._run raises an error if that happens, but the raised
error is not handled. This refactor catches this error to ensure the
original behavior happens, that is if a ref is not found, treat it as a
commit hash and call SCM.get_full_commit_hash.
Signed-off-by: Chenxiong Qi <cqi@redhat.com>
In particular, test to see if we can pass a branch name with shell
characters, and get MBS to inadvertently execute malicious code.
The test shows that doing this in a straightforward way is not possible
and should guard against any future regressions.
Fixes#329.
