Fixes for various Deltacloud::API middleware issues

These patches address various issues Winged Monkey folks got when they tried to use 1.1.2 as a Rack middleware.

Two major issues addressed here:

* Deltacloud[:deltacloud].require! need to require the new 'mock_initializer' to properly setup Mock storage directories
* The `driver` method exists silently with `nil` value if NameError exception occurs in driver (see 1)).
* We **should** not pollute the global Ruby namespace with `include Deltacloud` **outside** the class or module.

JIRA related to these issues:

https://issues.apache.org/jira/browse/DTACLOUD-507
https://issues.apache.org/jira/browse/DTACLOUD-540
https://issues.apache.org/jira/browse/DTACLOUD-517