sharder: add find_compactible_shard_sequences unit test
sharder: add find_compactible_shard_sequences unit test

This method was previously only indirectly covered by
test_manage_shard_ranges.  Add unit tests in test_sharder.

Change-Id: I9d0403f6dfa7a988e79f79a38ff713d05476cb84

tipabu/swift,tipabu/swift,openstack/swift,openstack/swift,tipabu/swift,openstack/swift,tipabu/swift,openstack/swift