ec2 start and stop aliases complain about extra arguments #98

The "aws ec2 start" and "aws ec2 stop" aliases fail reporting that --instance-ids is unexpected, and additional parameters are not permitted.

I'm sorry, Dave. I'm afraid I can't do that.Additional properties are not allowed (u'instance_ids' was unexpected)
Failed validating 'additionalProperties' in schema:
{'additionalProperties': False,
'properties': {u'AdditionalInfo': {u'description': u'Reserved.',
u'type': [u'string', 'null']},
u'DryRun': {u'description': u'Checks whether you have the required permissions for the action, without actually making the request, and provides an error response. If you have the required permissions, the error response is DryRunOperation. Otherwise, it is UnauthorizedOperation.',
u'type': [u'boolean', 'null']},
u'InstanceIds': {u'description': u'One or more instance IDs.',
u'required': True,
u'type': u'array'},
u'action': {u'default': u'start_instances',
u'immutable': True,
u'type': u'string'},
u'cls': {u'default': u'ec2', u'type': u'string'},
u'content_version': {u'description': u'Git revision of the pack content to use for this action execution (git commit sha / tag / branch). Only applies to packs which are git repositories.',
u'required': False,
u'type': [u'string', 'null']},
u'debug': {u'default': False,
u'description': u'Enable runner debug mode.',
u'required': False,
u'type': u'boolean'},
u'env': {u'description': u'Environment variables which will be available to the script.',
u'type': [u'object', 'null']},
u'headers': {u'type': [u'string', 'null']},
u'log_level': {u'default': u'DEBUG',
u'description': u'Default log level for Python runner actions.',
u'enum': [u'AUDIT',
u'CRITICAL',
u'ERROR',
u'WARNING',
u'INFO',
u'DEBUG'],
u'type': u'string'},
u'module_path': {u'default': u'boto3',
u'immutable': True,
u'type': u'string'},
u'timeout': {u'default': 600,
u'description': u"Action timeout in seconds. Action will get killed if it doesn't finish in timeout seconds.",
u'type': u'integer'}},
'title': u'ec2_start_instances',
'type': 'object'}
On instance:
{u'action': u'start_instances',
u'cls': u'ec2',
u'debug': False,
u'instance_ids': u'i-0689c67653ea35cc8',
u'log_level': u'DEBUG',
u'module_path': u'boto3',
u'timeout': 600}

This is due the action expecting parameter InstanceIds. Also the unpacking of the result does not match what is received in response to a start or stop ec2 instance command.

I have a proposed PR that fixes these existing aliases.