update the relative path of api_extensions_path

the previous path 'unit/extensions' could not be found correctly.

Change-Id: Ic8e658e651e99e57d19f6c3390db89650600decd
Closes-Bug: 1379711
Updated from global requirements

Change-Id: Ib0c8c561427f141583d677e86a76cbfe4e2be606
Merge "Updated from global requirements"
Merge branch 'master' of https://github.com/openstack/quantum