upgrade: get version from suffix of branch name (#1416)
upgrade: get version from suffix of branch name (#1416)

Currently we assume the branch name is origin/branch-xxx.x, it works well in
formal jobs. When I test with personal branch origin/upgrade-ipv6-2019.1, the
version can't be identified correctly.

This patch changed to get version from suffix of branch name, it's more
flexible.

Signed-off-by: Amos Kong <eb01d8f828a6c9a20be4534e72e049aaf41503df@scylladb.com>
scylladb/scylla-longevity-tests,scylladb/scylla-cluster-tests,scylladb/scylla-longevity-tests,scylladb/scylla-cluster-tests,scylladb/scylla-cluster-tests,scylladb/scylla-cluster-tests,amoskong/scylla-cluster-tests,amoskong/scylla-cluster-tests,amoskong/scylla-cluster-tests,scylladb/scylla-longevity-tests,scylladb/scylla-cluster-tests,amoskong/scylla-cluster-tests,amoskong/scylla-cluster-tests