FIX: stop causing unknown status error from user stop

[ZLLentz]

Description

Make sure we call stop with success=True in the positioner widget when the user clicks on the stop button.

Motivation and Context

If we call stop with success=False, it marks the status as failed and gives us an unknown status error. This is a problem because we can confuse ourselves immediately. The screen should not report planned stops as unknown errors.

success is an expected keyword in the bluesky hardware interfaces: https://blueskyproject.io/bluesky/hardware.html#bluesky.protocols.Stoppable.stop

Here is the ophyd source path where the status gets marked as failed if we call with success=False (the default):

• https://github.com/bluesky/ophyd/blob/0e8acb3df3d17e0ab7aa2cc924831f4a0c580449/ophyd/positioner.py#L107
• https://github.com/bluesky/ophyd/blob/0e8acb3df3d17e0ab7aa2cc924831f4a0c580449/ophyd/positioner.py#L218-L220
• https://github.com/bluesky/ophyd/blob/0e8acb3df3d17e0ab7aa2cc924831f4a0c580449/ophyd/positioner.py#L209
• https://github.com/bluesky/ophyd/blob/0e8acb3df3d17e0ab7aa2cc924831f4a0c580449/ophyd/status.py#L374-L381

Contributes to https://jira.slac.stanford.edu/browse/LCLSPC-397

How Has This Been Tested?

Added relevant test cases.

Where Has This Been Documented?

I think this is a bugfix that doesn't need a specific docs call-out.

[ZLLentz]

Two tests fail due to a small oversight in pydm v1.17.0 that is fixed in master. I'm going to xfail those tests for now and move forward.

[ZLLentz]

The travis keeps failing because of a bug in pydm v1.17.0, but maybe you saw a different issue