Two new validations are added:
1. A condition can not be only "negative". For example, instead of: "not alarm_on_instance" one should use "instance and not_alarm_on_instance"
2. There should be an entity that is common to all parts of an "or" condition. For example, this is illegal: "alarm1_on_host or alarm2_on_instance"
Change-Id: I209155ade48ba740642670891c11aeef0868197c
Implements: blueprint support-external-actions