Implement rescue mode support for Rackspace

Create real and mock rescue and unrescue methods for Rackspace compute V2
Create tests for rescue and unrescue methods
Rectify issues with tests and status

* Since the server will remain in ACTIVE state for up to a few minutes, do not
  set the status (to prevent a situation where the state bounces between
  PREP_RESCUE and ACTIVE).
* Add format() test for the call to #rescue
* Remove extraneous sleep from the test against #unrescue
* Remove immediate tests for state.  Rather, depend upon the wait_for function.
[cloudstack] add delete_snapshot request mock, fix delete_snapshot description comments
[cloudstack] add list_snapshots request mock
[cloudstack] add test volume to mock data
[cloudstack] tests, add snapshots_attributes to cloudstack provider config
[cloudstack] tests, fix snapshot test
[cloudstack] tests, remove unreachable code in snapshot test, add testcase for volume relation
[vsphere] Use Fog.mock? as the other providers
Specs can set Fog.mock! without setting the env var
[vsphere] Use find_raw_datacenter instead of get_raw_datacenter

find_raw_datacenter uses the cache of datacenters in list_datacenters, speeding it up. Calls to get_raw_datacenter if not cached
Merge pull request #1769 from maestrodev/fog_mock

[vsphere] Use Fog.mock? as the other providers
Merge pull request #1770 from maestrodev/find_raw_datacenter

[vsphere] Use find_raw_datacenter instead of get_raw_datacenter
[cloudstack] add create/delete disk_offering mocks
[cloudstack] add disk_offering model tests
Merge pull request #1753 from cwuest/master

[Rackspace | ComputeV2] Add calls to enter and exit rescue mode
Fix non-circular-require warnings

This fixes miscellaneous warnings in fog including unused variables,
indentation mismatch and one warning for a duplicated attr_reader.
[cloudstack] fix typo in declaration model
Merge pull request #1774 from drbrain/fix_warnings

Fix non-circular-require warnings
Merge pull request #1768 from dm1try/cloudstack_fix_snapshot_tests

[cloudstack] fix snapshot tests
Merge pull request #1771 from dm1try/cloudstack_add_disk_offering_model

[cloudstack] add disk offering model