Enable UTs to run on OSX
Enable UTs to run on OSX

OSX uses the dylib extension for shared libraries. Check which OS the
code is running on and change the import extension for Darwin based
OSes.

Change-Id: I93558e9bfb6dc8f1dd0db74c45b4c7a8937211c3

noironetworks/networking-cisco,noironetworks/networking-cisco,openstack/networking-cisco,openstack/networking-cisco