RTSPCameraAgent: connection robustness

[davidvng]

Description

• Move connection to camera stream to its own function
• Continue loop instead of stopping acq process when snapshot fails
• Add connected to session.data and OCS feed

Motivation and Context

Resolves #809

How Has This Been Tested?

Tested on daq-dev

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.

[BrianJKoopman]

Thanks for this! There's one bug with the connected status, but otherwise looks good.

[BrianJKoopman]

This is returning a tuple if cap doesn't open, which results in not cap: evaluating to False down on line 226, so this will always result in connected = True. It made sense to return this tuple within the process, since that's what ocs needs, but now that it's moved best to just return None, that will evaluate the connected check correctly.

>>> cap = False, "Could not open RTSP stream"
>>> connected = True
>>> if not cap:
...     connected = False
...
>>> print(connected)
True

[BrianJKoopman]

return False -> return False, "Cannot connect to camera"