Changes trove_client.client.HTTPClient to
trove_client.HTTPClient

Reasons:
 - trove shell is not working.
 - troveclient.client is now imported as trove_client
   but while calling the method it has been called
   as trove_client.client

Changes:
- Changes trove_client.client.HTTPClient to
  trove_client.HTTPClient in troveclient/v1/client.py

Change-Id: I12b0a0d9792f69ad04a17c36a8de134f233afc85
Closes-Bug: #1259882