Bring some missing functions from master to stable.

testing/sdk_cmd.py

@@ -290,6 +290,24 @@ def task_exec(task_name: str, cmd: str, return_stderr_in_stdout: bool = False) -
     return rc, stdout, stderr
 
 
+def service_task_exec(service_name: str, task_name: str, cmd: str, return_stderr_in_stdout: bool = False) -> tuple:
+    """
+    Invokes the given command on the named SDK service task via `dcos task exec`.
+    :param service_name: Name of the service running the task.
+    :param task_name: Name of task to run 'cmd' on.
+    :param cmd: The command to execute.
+    :return: a tuple consisting of the task exec's return code, stdout, and stderr
+    """
+
+    # Contrary to CLI's help text for 'dcos task exec':
+    # - 'partial task ID' is only prefix/startswith matching, not 'contains' as the wording would imply.
+    # - Regexes don't work at all.
+    # Therefore, we need to provide a full TaskID prefix, including "servicename__taskname":
+    task_id_prefix = '{}__{}__'.format(sdk_utils.get_task_id_service_name(service_name), task_name)
+
+    return task_exec(task_id_prefix, cmd, return_stderr_in_stdout)
+
+
 def resolve_hosts(marathon_task_name: str, hosts: list, bootstrap_cmd: str='./bootstrap') -> bool:
     """
     Use bootstrap to resolve the specified list of hosts

testing/sdk_utils.py

@@ -47,6 +47,13 @@ def get_foldered_name(service_name):
     return '/test/integration/' + service_name
 
 
+def get_task_id_service_name(service_name):
+    '''Converts the provided service name to a sanitized name as used in task ids.
+
+    For example: /test/integration/foo => test.integration.foo'''
+    return service_name.lstrip('/').replace('/', '.')
+
+
 def get_zk_path(service_name):
     # Foldered services have slashes removed: '/test/integration/foo' => 'test__integration__foo'
     return 'dcos-service-{}'.format(service_name.lstrip('/').replace('/', '__'))