Add an environment_format.py like the template one

This to make the section checking mechanism less spread out
and more consistent. This can also be used by the global
environment loader.

Change-Id: I7ca7ad754fb702877dedc416a30f573d239933ad
Load deployer/global environment files at startup

This allows for a global environment that the deployer can use to set
their own defaults.
An example /etc/heat/environment.d/x.yaml

resource_registry:
  "OS::Quantum*": "OS::Neutron*"
  "AWS::RDS::DBInstance": "file:///etc/heat/templates/AWS_RDS_DBInstance.template"

Change-Id: Iee647a109e5a41d41cd4a79909c6edaca0d17b87
Use the global environment to define AWS::CloudWatch::Alarm

This will make it easier for the deployer to define the default
implementation.

Change-Id: If1a8dceb4ad2cade90a56f16dd450e571425c4a6
Merge "Add an environment_format.py like the template one"
Merge "Load deployer/global environment files at startup"
Merge "Use the global environment to define AWS::CloudWatch::Alarm"