[openstack|storage] Added support to impersonate other accounts

The patch would allow to impersonate other accounts if you have
an admin role:

     require 'fog'
     require 'pp'

     auth_url = 'https://identity.test.lan/v2.0/tokens'
     user = 'admin@test.lan'
     password = 'secret'

     id = Fog::Identity.new :provider => 'OpenStack',
                            :openstack_auth_url => auth_url,
                            :openstack_username => user,
                            :openstack_api_key  => password

     st = Fog::Storage.new :provider => 'OpenStack',
                           :openstack_auth_url => auth_url,
                           :openstack_username => user,
                           :openstack_api_key  => password

     id.tenants.each do |t|
       puts "Changing account to #{t.name}"
       st.change_account "AUTH_#{t.id}"
       # list account containers
       pp st.directories
       # We could also head the account and get usage information
       pp st.request :method => 'HEAD'
     end
[openstack|storage] added missing mocks
get rid of bucket/directory delete - not allowed for IA
add IA specific headers for file
get rid of versions from IA
Merge remote-tracking branch 'upstream/master' into internet_archive
missed one
fix tests, found a few differences with S3
fix 1.8.7 error, oops
add ovirt quota support
[rackspace] adding auth 2.0 to compute, databases, dns, load balancers, cloud block storage
[rackspace|blockstorage] adding Cloud Block Storage Examples
Merge branch 'default_endpoint' of github.com:rackspace/fog into auth_deux
[rackspace|compute_v2] updated detach volume to use :rackspace_region to specify region
[rackspace] updated service endpoint handling; improved service endpoint tests
[rackspace] moving require 'fog/rackspace/service' to fog/rackspace
[rackspace] fixing auth 20 issue where tenant id is not being appended to the service url
Merge branch 'master' of github.com:fog/fog into auth_deux
Merge branch 'master' of github.com:fog/fog into auth_deux
rackspace|compute_v2] removing superfluous note from compute_v2 documentation