Sid sprint88 merged knife openstack

I merged following PR's to this branch:
https://github.com/opscode/knife-openstack/pull/55
https://github.com/opscode/knife-openstack/pull/58
https://github.com/opscode/knife-openstack/pull/51
https://github.com/opscode/knife-openstack/pull/57
https://github.com/opscode/knife-openstack/pull/50

Note: Resolved merge conflict for https://github.com/opscode/knife-openstack/pull/50