Fog::Model#wait_for: eliminate inner retry loop

AWS frequently takes more than 3 seconds for an instance to appear.
Rather than having the overlapping timeouts for reload and
instance_eval, simply make them both occur with the same timeout.

 + Prevents spurious failures when waiting for AMI
 + Easier to follow flow
[openstack] Retrieve supported API version for Image & Network services
[openstack|compute] Add volume attachment methods
[rackspace] updated getting_started.md to use source 'https://rubygems.org' rather than :rubygems.
[rackspace|compute_v2] added bootstrap and ssh section to compute documentation.
mend
[rackspace] tweaking getting started page
[rackspace] adding note about credentials in the getting started document
[rackspace] revising getting started page
[rackspace|compute_v2] updated the bootstrap section of the compute_v2 documentation.
Updated gem spec to require json rather than multi_json; Fog::JSON will attempt to load and use multi_json first and then fallback to require json; removed hard coded references to multi_json
Merge branch 'master' of github.com:fog/fog into json_lib
Adding multi_json to GemFile as it is now an optional dependency for the gem
Added tests for Fog::JSON; Added Fog::JSON::LoadError class; Updated all MultiJson references to Fog::JSON
Merge branch 'master' of github.com:fog/fog into json_lib
[core] fixing brittle json test
[openstack|compute] Add volume method to server model
[openstack|compute] Add volume tests
Merge pull request #1718 from rackspace/boot_doc

[Rackspace] Revising Getting Started Documents
[xenserver|compute] update changelog