CIMI: Added VolumeCreate model

Signed-off-by: Michal fojtik <mfojtik@redhat.com>
TrackedAt: http://tracker.deltacloud.org/patch/15544d24bd245a6d5ecee21e0efb3aaa2f3856f2
CIMI: Added ref_id helper to Base class

The ref_id(url) will extract the last segment of the
URL and return it as an 'id'.

FIXME: We should use ctx to return the ID of resource properly.

Signed-off-by: Michal fojtik <mfojtik@redhat.com>
TrackedAt: http://tracker.deltacloud.org/patch/90eb17744273b3e64b01808f7692fe57c4cff097
CIMI: Use class.superclass instead of opts[:class]

Under latest MRI 1.9.3 the 'opts[:class]' is not visible
to 'find' method and it is reported as 'method missing'

With 'class.superclass' we get access to the original class
we used to create Ref.

Signed-off-by: Michal fojtik <mfojtik@redhat.com>
TrackedAt: http://tracker.deltacloud.org/patch/a24aefe5f66b14b2be6fbc91c0eb2338c4f59a44
CIMI models: move validate! to CIMI::Model::Resource

It also needs to be available for collections, which do not derive from Base
CIMI Model: do not trip over Fixnums during validation

There's no Fixnum#empty?; convert everything to a String before checking
for emptiness.
CIMI models (VolumeConfig): add missing type attribute
CIMI tests: href on MachineConfig is now a proper attribute

Fixes a test failure
CIMI (MachineCreate): pass initialState to driver
CIMI tests (rmd4_test): simplify the code a little