[google|monitoring] Add support for Google Cloud Monitoring

- Add models, requests, tests & examples for Timeseries
- Add models, requests, tests & examples for TimeseriesDescriptors
- Add models, requests, tests & examples for MetricDescriptors
Make possible to get credentials value, since it's needed to start a console connection
Clean up Excon::Errors::SocketError::EOFError warning in vcloud_directory

Every time I make a connection with the vcloud_director provider I get this warning:

/Users/mray/.chgems/vchs/.gem/ruby/2.1.2/gems/fog-1.23.0/lib/fog/vcloud_director/compute.rb:372: warning: toplevel constant EOFError referenced by Excon::Errors::SocketError::EOFError
Merge pull request #3066 from frodenas/gce_monitoring

[google|monitoring] Add support for Google Cloud Monitoring
Merge pull request #3072 from mattray/vcloud_director_eoferror

Clean up Excon::Errors::SocketError::EOFError warning in vcloud_director
Merge pull request #2946 from fmbiete/xenserver_credentials

XenServer - attr_reader for Compute > connection > credentials
remove leading slash from Rackspace compute_v2 request paths
Merge pull request #3074 from pdxfixit/master

remove leading slash from Rackspace compute_v2 request paths
[dynect|dns] Let job_poll_timeout be specified.
[google|compute] Refactor Compute to use the new Shared module

Commit d801b27 introduced a new Shared module with logic to initialize
a google_client_api and to make requests.

This commit refactors Compute to use the new Shared module.
Merge pull request #3081 from dpiddy/dynect-dns-specify-job-poll-timeout

[dynect|dns] Let job_poll_timeout be specified.
Merge pull request #3080 from frodenas/gce_shared

[google|compute] Refactor Compute to use the new Shared module
Merge remote-tracking branch 'new-upstream/master' into gce_l7

Conflicts:
	lib/fog/google/requests/compute/delete_backend_service.rb
correct files changes accidentally