Checks min requirements before trying to launch an instance

  Server side version.

An image can have properties min_ram/min_disk that prevents
to launch instance with a flavor doesn't have enough resources.

Notes:
  Adds in create_instance.py a solution to check requirements
  Adds in glance_data.py ram/disk properties for and image (default:0)
  Fix in tests.py, some ut needed to be updated
  Adds in tests.py two new tests to check min_disk and min_ram

Change-Id: Ia4a9e4ed729321f70de93296e3257898a52c8e32
Implements: blueprint image-flavor-minimun-requirements
Merge "Checks min requirements before trying to launch an instance"