Add a GCM test with non-standard nonce length.

AES-GCM should have a 12-byte nonce. However, non-standard nonce sizes
are defined by NIST and, although they are a bad idea, people have used
them because they've confused an IV with an nonce and passed in a
16-byte nonce.

This change adds a test for this.

Change-Id: If1efa1aaa19f0119ad4cab9a02a6417c040f45b2