JCLOUDS-457: Part of the code has been cleaned up

On the last commit we added TestUtils class. On this commit
the VaultNameValidator and the ThreeHashTest tests make use
of it.

GlacierClientMockTest was not using GlacierHeaders references.
This commit fixes this problem too.

In addition, the AWSRequestSignerV4, the TreeHash and the
VaultNameValidator classes are now final.