Allow simultenious action execution

Currently there can be only one action running per environment at a time. Actions are often called by 3rd party systems that cannot wait for environment to become ready. Some of the actions require immediate response and/or have no side effects and safe to be run in parallel. The proposed change is to allow simultaneous execution of actions in single environment.

The following issues need to be addressed:
1) Simultaneous actions may do concurrent modifications to object model. After task execution engine should send a json-patch of what have changed during deployment/action invocation rather than complete object model. Then API could apply the patch to a last known object model state
2) Make use of distributed lock management system such as ZooKeeper/etcd/council etc to implement distributed locks in MuranoPL to protect resources from incompatible concurrent modifications by simultaneous actions