Add a message in "Ethercat Master" diagnostics when unable to reset motors (ros ticket #4475)

[ahendrix]

When a user is unable to reset motors, there should be an error message in the "Ethercat Master" diagnostics saying "Unable to reset motors. Restart pr2-etherCAT" or something.

Users can get confused when the "reset_motors" service call doesn't work.

trac data:

• Owner: dking
• Reporter: watts
• Reported at: Sat Jun 26 00:15:12 2010
• URL: https://code.ros.org/trac/wg-ros-pkg/ticket/4475

[ahendrix]

[dking] r40035

ethercat hardware doesn't known that it reset motors won't work in some cases. However it can tell that the motors halted due to error condition soon after a reset.
When this happens I report the following error: {{{ Motors halted soon after reset }}}

I don't agree with the "Restart pr2-etherCAT" message. If the run-stop is pressed and restarting pr2_etherCAT will not work.

I think we need a higher-level process to use information from multiple sources (pr2_etherCAT, power_node, ...) to make an intelligent decision about what to do for a specific error.

Right now the higher level process is the user, though we might want to make a FAQ about what to do for specific errors.

[ahendrix]

[watts] Or we can push this up to the diagnostic aggregator, which is probably the right answer. I want to make an aggregator before d-turtle. We should figure out the user interface for that at some point.