decode_to_md5_test: fixes and runs quick encode and checks decode

This test checks if there's any basic change to the bitstream or default
encoder by running an encode and checking that the md5 from the decode
doesn't change.

Any change to the default encoder or bitstream should be accompanied by
a change to the md5 in this file.

Change-Id: Ibdd5a1442296fd3e946823ec1f43e8ac4e66dd34