Enforce length checking for instance name field

Add the max_length checking for instance name field in Update Instance.
Also changed the max_length value from 80 to 255 in Create Instance
to match the backend's restriction.

Change-Id: I52398a13a545449699a7209db49c06859daa9463
Closes-Bug: #1279590
Merge "Enforce length checking for instance name field"