implement exec

Resolves #593

Signed-off-by: Tomas Tomecek <ttomecek@redhat.com>

compose/container.py

@@ -216,6 +216,12 @@ class Container(object):
     def remove(self, **options):
         return self.client.remove_container(self.id, **options)
 
+    def create_exec(self, command, **options):
+        return self.client.exec_create(self.id, command, **options)
+
+    def start_exec(self, exec_id, **options):
+        return self.client.exec_start(exec_id, **options)
+
     def rename_to_tmp_name(self):
         """Rename the container to a hopefully unique temporary container name
         by prepending the short id.