Directly use self.flavor
Make image optional and add rudimentary support for block devices

The image keyword is now optional and defaults to None. The
block_devices keyword will map to the block_device_mapping_v2 in
novaclient. Some simple parsing will happen to allow a higher level use
than what --block-device presents in the shell.
Refactor _getImage to allow any image callable to be used

This may eventually be extended to work with block devices.
Add block devices to kwargs for servers.create
Combine all test auth data into one dict

Combined all of the test auth keywords into a dict to make setting up a
buildslave slightly less tedious.
Simplify more redundant test args

Most creations of the slave now can use the shorter **self.bs_args.
Test OpenStackBuildSlave.stop_instance
Test basic block_devices functionality
Add a kwargs to OpenStackBuildSlave

Add a kwargs to allow people that know what needs to be passed to
servers.boot the option to do so.
Add release notes and documentation
Fix release notes

I missed a blank line.
Make _getImage a static method
Use nova_args parameter to hold extra options for novaclient
Merge Cray/buildbot:openstack-block-device (PR #1221)

Conflicts:
	master/docs/manual/cfg-buildslaves.rst (merged to cfg-buildslaves-openstack.rst)

+autopep8