EC2Signer to sign cfn calls.

This is identical to the copy in heat and python-keystoneclient.
A copy is made here to avoid creating a dependency.

Change-Id: Ia4533d1337b56e9fbe2b2d8f5f9c106be556de08
Move FakeHTTPResponse to its own fakes file for reuse

Change-Id: Ibd041551d200230b1394cfe6dcd7afa093318718
No longer use boto for metadata retrieval

Now makes the request using the minimal httplib based client

Change-Id: I7e64d497179763faabf1192d1a4d5f96679da20b