oeqa/utils/gitarchive: Return tag name and improve exclude handling

Tweak the gitarchive exclude handling not to error if excluded files
don't match.

Also return the tagname created so that other code can then use it.

(From OE-Core rev: 0a5b4fabf8bf9b559295bb4d2583809ca11522f4)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit 1adba3430faffdf6217b6a00533a3b48a9388abc)
Signed-off-by: Steve Sakoman <steve@sakoman.com>