Fix wrong request json body of subnet creation

Actual request should not have nested subnet entry.

Change-Id: I70acf509fb1604b066827c39c18ae56266b3a5cf
Close-Bug: #1329098
Replaced the JSON response code in image-api

Correct Json response for adding a tag to an image
in image-api should be 204. Replaced the earlier
Json response 200 with 204.

Change-Id: Icfc307a04fab038b113b50f584aaf41cdbea26ce
Closes-Bug: #1327767
Merge "Replaced the JSON response code in image-api"
Merge "Fix wrong request json body of subnet creation"