add ping_BBB function in wiregrid_encoder

[sadachi5]

Description

Add ping_BBB() command in the wiregrid_encoder agent.
This function checks the connection to the beagleboneblack for the wiregrid.
It returns True or False.

Motivation and Context

This function is useful for the sorunlib script for wiregrid to check the connection to the BBB before the calibration.

How Has This Been Tested?

The new function has not been tested yet.

The doc of wiregrid_encoder was modified.
In socs/requirements.txt, ping3 was added for ping_BBB() function.
--ip-adderss is added in the arguments for the wiregrid_encoder agent.
The argument should be added also in the ocs-site-config.

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]

We've been talking offline, but just for completeness here, I'd like to move the monitoring in a different direction. This ping doesn't tell us much beyond the host being up. A monitor of the UDP stream (possibly with additional health status packets added) is really what's needed. I'm going to close this PR, and drop references to this task in the sorunlib implementation.