Added post method to TenantClient

self.client.post() appeared to not be routed through the tenant, so I was getting
404's on all my urls. 
Override of post() in request factory. Methods now return requests.

get() and post() both need to set the HTTP host in **extra to be routed through the tenant.

The request factory was processing the requests instead of returning them for use in testing.
Merge pull request #23 from timothyshaw/master

Updated TenantClient and TenantRequestFactory to support post() method