VNF creation with image name and checksum working properly. Fixes bug 73....

VNF creation with image name and checksum working properly. Fixes bug 73. Added new tests for this feature. Openmano client modified to allow modifying image name and checksum

Change-Id: I6153fab0241778cba34414c8e45669cd40119eed
Signed-off-by: garciadeblas <gerardo.garciadeblas@telefonica.com>