Merge pull request #751 from theotherjimmy/mbed-dm-help-fix

Allow downstream impl of `mbed dm` to print help

Author: theotherjimmy

mbed/mbed.py

@@ -2942,6 +2942,7 @@ def test_(toolchain=None, target=None, compile_list=False, run_list=False,
     dict(name='--build', help='Build directory. Default: build/'),
     dict(name='--source', action='append', help='Source directory. Default: . (current dir)'),
     help='device management supcommand',
+    add_help=False,
     hidden_aliases=['dev-mgmt', 'dm'],
     description=("Manage Device with Pelion"))
 def dev_mgmt(toolchain=None, target=None, source=False, profile=False, build=False):