PackageParser: Add support for parsing codeNames with fingerprints.

In addition to supporting manifest declared codenames of the form
"[codename]", also support codenames of the form "[codename].[fingerprint]".

Also makes cosmetic changes to PackageParserTest to produce better
failure messages when the test fails.

Test: PackageParserTest

Change-Id: If5e38614a1a3aa04035f14acfda41d0c1cd86e15