claim estop on power on only if isn't already acquired (#79)

For spot_driver with estop, if power_off is called, and power_on is called, driver crashes as an error is thrown as it tries to reset estop.
Prevent this case.

Co-authored-by: bhung-bdai <[email protected]>

Author: skpawar1305

spot_wrapper/wrapper.py

@@ -1284,8 +1284,8 @@ def power_on(self) -> typing.Tuple[bool, str]:
         """
         # Don't bother trying to power on if we are already powered on
         if not self.check_is_powered_on():
-            # If we are requested to start the estop, we have to acquire it when powering on.
-            if self._start_estop:
+            # If we are requested to start the estop, we have to acquire it when powering on. Ignore if estop is already acquired.
+            if self._start_estop and self._estop_keepalive is None:
                 self.resetEStop()
             try:
                 self._logger.info("Powering on")