Create a common function for method _parse_network_vlan_ranges used
by plugins.

The _parse_network_vlan_ranges method does the same thing for the
linuxbridge, ovs, and hyperv plugins. Create a common function for
the plugins to use instead. This paves the way for improving vlan
range verification (see #1169266) in one place.

Fixes Bug #1177428

Change-Id: Ie8c20807e9146dd9c8bc011dd3a4dc10ec871e0b
Merge "Create a common function for method _parse_network_vlan_ranges used by plugins."