Shorten the path of the nicira nvp plugin.

 * s+[/.]nicira_nvp_plugin++
 * Backwards compatibility is maintained by importing the
   nicira package as nicira_nvp_plugin in the plugins package.
 * It may be necessary to remove stale .pyc/.pyo files under the
   nicira path after applying this patch.
 * DocImpact
 * Addresses bug 1166307

Change-Id: I241a2a75106398506b01bcb7a6ddbaafa1b7bd30
Merge "Shorten the path of the nicira nvp plugin."