[vsphere] allow to create a vm with multiple disks.

unitNumber has to be unique.
[docs::aws::storage] added [] to make it pretty
[docs::aws::storage] yard doc syntax fix
[docs::aws::storage] reformatted copy_object
Merge pull request #1433 from westonplatter/aws_docs

[docs::aws::storage] fixed some syntax and formatted a request
[docs::aws::storage] reformatted delete requests
Merge pull request #1437 from ohadlevy/vsphere-multi-disk

[vsphere] allow to create a vm with multiple disks.
Merge pull request #1436 from westonplatter/master

[docs::aws::storage] reformatted fog/aws/storage/requests delete
adding support for rackspace loadbalancer content caching
Merge pull request #1438 from luizfar/add_content_caching_to_load_balancer

adding support for rackspace loadbalancer content caching
WIP: vsphere: Allow listing virtual port groups

A bit more background: currently fog supports the Network[1], but there's
also DistributedVirtualPortgroup[2] which extends Network[1].

This has had limited testing and may not be perfect, but in the current
situation loading a DistributedVirtualPortgroup into the model will die
because the backing has no property network.

[1]: http://pubs.vmware.com/vsphere-51/index.jsp?topic=%2Fcom.vmware.wssdk.apiref.doc%2Fvim.Network.html
[2]: http://pubs.vmware.com/vsphere-51/index.jsp?topic=%2Fcom.vmware.wssdk.apiref.doc%2Fvim.dvs.DistributedVirtualPortgroup.html
WIP: vsphere: Support multiple NIC backings

With this commit create_vm tries to detect if the network is a
DistributedVirtualPortgroup[1]. If it is it will create the appropriate
backing (VirtualEthernetCardDistributedVirtualPortBackingInfo). If it's
not it will fall back to the regular backing
(VirtualEthernetCardNetworkBackingInfo).

Known issues:
* If a DVS is inside a folder instead of directly under the DC
  get_raw_network will not find it.
* It is possible to assign network permissions to a
  DistributedVirtualPortgroup, but not to the DistributedVirtualSwitch.
  In that case you can't read its UUID and it fails with an exception.

[1]: http://pubs.vmware.com/vsphere-51/index.jsp?topic=%2Fcom.vmware.wssdk.apiref.doc%2Fvim.dvs.DistributedVirtualPortgroup.html