Implement support for SSM parameter store

This commit adds initial support for the Simple System Manager client.

It currently only mocks the following api endpoints:
 - delete_parameter()
 - put_parameter()
 - get_parameters()

moto/ssm/responses.py

@@ -0,0 +1,56 @@
+from __future__ import unicode_literals
+import json
+
+from moto.core.responses import BaseResponse
+from .models import ssm_backends
+
+
+class SimpleSystemManagerResponse(BaseResponse):
+
+    @property
+    def ssm_backend(self):
+        return ssm_backends[self.region]
+
+    @property
+    def request_params(self):
+        try:
+            return json.loads(self.body)
+        except ValueError:
+            return {}
+
+    def _get_param(self, param, default=None):
+        return self.request_params.get(param, default)
+
+    def delete_parameter(self):
+        name = self._get_param('Name')
+        self.ssm_backend.delete_parameter(name)
+        return json.dumps({})
+
+    def get_parameters(self):
+        names = self._get_param('Names')
+        with_decryption = self._get_param('WithDecryption')
+
+        result = self.ssm_backend.get_parameters(names, with_decryption)
+
+        response = {
+            'Parameters': [],
+            'InvalidParameters': [],
+        }
+
+        for parameter in result:
+            param_data = parameter.response_object(with_decryption)
+            response['Parameters'].append(param_data)
+
+        return json.dumps(response)
+
+    def put_parameter(self):
+        name = self._get_param('Name')
+        description = self._get_param('Description')
+        value = self._get_param('Value')
+        type_ = self._get_param('Type')
+        keyid = self._get_param('KeyId')
+        overwrite = self._get_param('Overwrite', False)
+
+        self.ssm_backend.put_parameter(
+            name, description, value, type_, keyid, overwrite)
+        return json.dumps({})