Add validate image member method to behaviors

*Added validate_image_member method to images behaviors
*Added messages class to contansts
*Added error_message to constants to be used with validate_image_member method
*Updated error_message to ERROR_MSG for consistency in constants module
*Removed constants module from the common package since images only uses it
*Added validate_image method to images behaviors
*Updated valid_image_member method to account for fixture and behavior changes
*Fixed rebase issues

Change-Id: Ieefde29c79c01dfa86295cd384d6f75e2412e82b