No retries when sending a motor test command

#### Issue details
Sometimes when using wireless connection to FC and clicking on motor test button the motor actually does two starts-stop cycles instead of single one. And after there is Error Communicating message box appears.

Even it is strongly advised to not to perform motor test with props on, this behavior is potentially dangerous without props too.

Looks like it happens because of retry function in doCommand routine.

My proposition is to not to use retries for motor test commands.

#### Platform
[x] Copter

Start by locating the motor test button handling and the doCommand routine mentioned in the issue, then trace how retries are applied to motor test commands over a wireless FC connection. Done means one motor start-stop cycle occurs and no Error Communicating message appears; verify the behavior on the Copter platform.

Written by the indexing model from the issue text.