Add upstream-branch and upstream-tag options
Add config file and command line options to specify the upstream branch
name and upstream tag format for build, export and remotebuild commands.
This is needed in order to be able to support different maintenance
models of non-native packages (with patch-generation enabled):
1. If upstream sources are imported with GBS, these options are not
needed
2. However, if maintainer uses upstream git tree directly, he needs to
be able to specify the tag format - otherwise gbp is unable to
create orig source archive or generate patches
Command line option takes preference over the config file.
Signed-off-by: Markus Lehtonen <markus.lehtonen@linux.intel.com>