Enhancement deuce context swift storage url

- Stores the storage_url in the Deuce Context under deuce.context.openstack.swift.storage_url
- Fixes the mocking for Swift Client so that it is enabled via a single variable in config.py so the user does not need to modify test code to turn it on/off.

Depends on PR #82 

JIRA #CBDEUCE-153
Correct, the swift mock is another implementation of the Disk Storage driver.

This change, however, makes it so that to enable mocking you don't have to switch the driver, just set "is_mocking" to true, and then the test code switches the driver.