[xenserver] added create_sr request (create Storage Repository)
[xenserver] added destroy_sr request (destroy Storage Repository)
[xenserver] added unplug_pbd request
[xenserver] added new requests to compute service

- unplug_pbd
- destroy_sr
- create_sr
[xenserver] added unplug method to PBD model
[xenserver] missing Pool model attribute, new methods

- Added missing suspend_image_sr attribute
- added default_sr getter/setter
- added suspend_image_sr getter/setter
- added generic set_attribute method
[xenserver] added new methods to StorageRepository model

- destroy/save operations
- generic set_attribute method
[xenserver|docs] Added new example that covers a Citrix KB ctx116324 article

Translated http://support.citrix.com/article/ctx116324 to fog/xenserver
added server metadata operations for Fog::Compute::RackspaceV2
refactored Fog::Compute::RackspaceV2 metadata to take collection as a parameter rather than using it as part of the method name.
change copy_object docs to YARD
fixing broken metadata tests
[xenserver] Use Nokogiri instead of slow REXML for parsing
Merge pull request #1443 from westonplatter/master

[docs::aws::storage] rdoc to yard formatted all get requests
[ecloud] improvements and some mocking
Merge pull request #1442 from deepj/xenserver-nokogiri

[xenserver] Use Nokogiri instead of slow REXML for parsing
Merge pull request #1446 from ehowe/master

[ecloud] improvements and mocking
[xenserver] updated create_sr request documentation, fixed default values
[xenserver|tests] Added create_sr request tests
[xenserver|tests] Added destroy_sr request tests