ds402: Skip explicit change to SWITCHED ON state. (#249)

The BaseNode402.homing() method tries to enter state SWITCHED ON upon
entry.  That's unnecessary, the application should handle these
transitions.  But more importantly, it actually fails in many cases,
namely if the previous state is SWITCH ON DISABLED, the default
power-up state of most devices.  There is an automatic way to reach
OPERATION ENABLED over multiple intermediate steps, but the library
does not know how to reach SWITCHED ON from any other state than
OPERATION ENABLED or READY TO SWITCH ON.  In addition, setting the
op_mode property will already change to SWITCHED ON only if coming
from OPERATION ENABLED (which is usually a good idea to avoid
unexpected movement).

Note that switching the operation mode to HOMING is actually safe in
any power state.

Author: acolomb

canopen/profiles/p402.py

@@ -306,7 +306,6 @@ def homing(self, timeout=TIMEOUT_HOMING_DEFAULT, set_new_home=True):
         :rtype: bool
         """
         previus_op_mode = self.op_mode
-        self.state = 'SWITCHED ON'
         self.op_mode = 'HOMING'
         # The homing process will initialize at operation enabled
         self.state = 'OPERATION ENABLED'