Add a general "raise_on_error" option to all terraform commands. If provided and
set to anything that evaluates to True, then TerraformCommandError (a subclass of
subprocess.CalledProcessError) will be raised if the returncode is not 0. The exception
object will have the following special proerties:
returncode: The returncode from the command, as in subprocess.CalledProcessError.
out: The contents of stdout if available, otherwise None
err: The contents of stderr if available, otherwise None
Terraform.output() no longer requires an argument for the output name; if omitted, it
returns a dict of all outputs, exactly as expected from 'terraform output -json'.
Terraform.output() now accepts an optional "full_value" option. If provided and True, and
an output name was provided, then the return value will be a dict with "value", "type",
and "sensitive" fields, exactly as expected from 'terraform output -json <output-name>'
Added tests for all of this new functionality...
