Summary: Add documentation for the KVM support for OpenVswitch

Modified the KVM installation instructions with an example on how to use
the openvswitch bridges.

Modified the Nicira NVP plugin documentation with support for KVM

Updated the Nicira NVP docs to mention that it can be configured using
the UI now.
Merge branch 'cloud-agent-with-openvswitch' of https://git-wip-us.apache.org/repos/asf/incubator-cloudstack into cloud-agent-with-openvswitch