Add python parsing library for network settings file.

Add python parsing library for network settings file.

Changes:
   - Implements network_settings.yaml file parsing in python.
   - Adds support for both IPv4 and IPv6 in network_settings.yaml
   - Adds support for api_network in network_settings.yaml
   - Removes bash library functions for network related functions.
   - Adds dependency to python34-yaml for apex-common package.

Note that support for ipv6 and api_network is not complete yet.
Proper configuriration of network environment and nic template
files will be added later.

Change-Id: I087f725dabedfef109c9de1f58ce2611da647e87
Signed-off-by: Feng Pan <fpan@redhat.com>