Support specifying upstream and additional branches to import via
SHA1s.
Check for pattern character '*' in provided patterns to determine which
to treat as patterns and which as explicit revisions.
Include additional test function to check converting all refs to SHA1s
as input, and an additional scenario to check passing in a relative ref
using '~' to pick a different commit to the head of the branch.
Change-Id: Ie6ad695a34307d96b95f81b017ba9f190bc258dc
Partial-Bug: #1547180
5f4038e268