modified image common type enums to be lower case

 - to be compatible with API defined headers, common types must be
   lowercase.

Change-Id: I2c472413ecc0b5e3e2b3c7b356894a78b81c13b6
Changes around security groups api

1. Added list-security-group and
 add-security-group methods to server client
2. Refactored security group request classes.
3. Added delete-security-group-rule method to
security group rule client

Change-Id: Ie0c4e6525b6f4066a8e31b4f1028e5baa94118b4
Merge "modified image common type enums to be lower case"