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
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
[vsphere|compute] fix incorrect filters.merge in networks model
Merge pull request #1742 from aussielunix/vsphere-bug-list-networks

[vsphere|compute] fix incorrect filters.merge in networks model
Merge pull request #1730 from rackspace/json_lib

[Core] Updated Fog::JSON to use JSON gem by default
add 2.0.0 to travis build list
Added pointers to provider specific documentation to README.md
Merge pull request #1744 from rackspace/provider_docs

Added pointers to provider specific documentation to README.md
Merge pull request #1699 from frodenas/openstack_get_version

[openstack] Retrieve supported API version for Image & Network services
[cloudstack] add disk_offerings, os_types mock data
[cloudstack] add list_os_types, list_disk_offerings request mocks
[cloudstack] list_os_types, list_disk_offerings request tests, rm pending
Merge pull request #1750 from dm1try/cloudstack_add_list_os_types_and_list_disk_offerings_mocks

[cloudstack] Add list os types and list disk offerings mocks
Merge pull request #1748 from maginatics/timeout2

Fog::Model#wait_for: eliminate inner retry loop