No 4 byte unicode allowed in image parameters

Image create or update with params containing 4 byte unicode characters
results in 400 server error code (instead of former 500).
Image name/location/tags/properties are validated this way

Change-Id: Ib0fcf2456f0996e8235983b361d1ee5f66136375
Closes-bug: #1370954
Merge "No 4 byte unicode allowed in image parameters"