Added a method for parsing host:port pairs.
Added a method for parsing host:port pairs.

The method works correctly with ipv6.
An alternative way would be to use urlparse, but urlparse
only works correctly starting with Python 2.7, so to be
compatible, we have to reimplement this part.

The method will be used for parsing Glance API server
addresses, RabbitMQ addresses and perhaps other things.

Change-Id: Ie5014891c6abcd80681a370d5dd94cb0406f7f61

emonty/oslo-packaging,WiFast/pbr,emonty/oslo-packaging,openstack-dev/pbr,redhat-openstack/pbr,redhat-openstack/pbr,JioCloud/pbr,varunarya10/pbr,citrix-openstack-build/pbr,klmitch/pbr,WiFast/pbr,citrix-openstack-build/pbr,JioCloud/pbr,openstack-dev/pbr,openstack-dev/pbr,citrix-openstack-build/pbr,klmitch/pbr,varunarya10/pbr