Take InstanceType for launchconfig res creation

Take the init value of InstanceType for launchconfig
resource creation, since heat will apply nova flavor
custom constraint for launchconfig resource,
see: https://review.openstack.org/#/c/134879/

Change-Id: I23c6032f49104880dc6b424d115ff437f698f5c6
Remove unnecessary parameters on create_volume API

Current Tempest client passes a null value to Nova's create_volume
API if tests don't specify description_name and metadata attributes.
However, that is wrong behavior because these attributes are optional
and Tempest doesn't need to specify them instead of specifying null
values. This behaivor will be a problem because Nova v2.1 API doesn't
allow this kind of values by strict input validation.

This patch makes create_volume API client skip passing null values
in this case.

Change-Id: I16249afeb254dfce1c4b155e2e3746500f6a9ea5
Merge "Take InstanceType for launchconfig res creation"
Merge branch 'master' of https://github.com/openstack/tempest