Add upstream-branch and upstream-tag options

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>