Add utility join_ipv4_segments and increment_ipv4_segments functions to
libcloud.utils.networking module.

Patch by Andrew Mann, Tomaz Muraus.
Add initial implementation of a base networking API with a reference drivers
for OpenStack Neutron and OpenStack Quantum.

Also add support for retrieving a networking driver to the OpenStack compute
driver.

Note: Base API hasn't been decided upon yet and is subject to change.