Allow fetching release from branch basename
In case fetching release information from the whole branch fails,
retry with just part of branch name delimited by '-'. This should
allow branches like rawhide-staging or f38-bz1234 to be recognized
as a supported staging branches.
Those are expected to be non-production, feature-only branches.
It should not allow to build these branches as a production build.
JIRA: RHELCMP-12565
Merges: https://pagure.io/fedpkg/pull-request/522
Signed-off-by: Petr Menšík <pemensik@redhat.com>