Port server password extension to v3 API Part 1

This changeset only copies the v2 implementation file into the
appropriate v3 directory unchanged. The copy as-is will not be
loaded by either the v2 or v3 extension loaders. The second
changeset will then make the changes required for it to work as a
v3 extension.

This is being done in order to make reviewing of extension porting
easier as gerrit will display only what is actually changed for v3
rather than entirely new files

Partially implements blueprint nova-v3-api

Change-Id: I8be578ed4fada25ec4a8aa8adb3addb0a3791f85
Merge "Port server password extension to v3 API Part 1"