Rename nicira configuration elements to match new naming structure

- Every config item prefixed with nvp is prefixed with nsx
- deprecation qualifiers are added to preserve bw compatibility
- nicira/nvp.ini is renamed to vmware/nsx.ini
- symlink nicira/nvp.ini is created to point to vmware/nsx.ini
- UT added to verify that nvp.ini and old config items can still
  parsed correctly; bw-compat will be dropped in Juno

Partial-implements blueprint nicira-plugin-renaming

Change-Id: I676b868e61064cc5ff17e2246e83ba5c5e4a3449
Merge "Rename nicira configuration elements to match new naming structure"