Recent GHA runs of the DDS tests are failing. This is an attempt to stabilize.

In general, GHA tasks run on only two cores and some of our tests use multiple processes and multiple threads and are therefore sensitive.

At least one problem seen is:

• The broadcaster broadcasts a device
• The client sees it in thread 1
• The client is waiting for devices in thread 2 (python)
  • Thread 2 is, every second, performing a query_devices() until it sees the device
  • Query devices sees the device (it's part of the devices that can be iterated on the device-watcher)
  • Thread 2 wakes up and tries to act on the device

But Thread 1 is not yet done initializing the device!

Changes:

• fix rspy.test.context initialization to []
• add "gha" to rspy.test.context using GITHUB_ACTIONS env var
  • i.e., you can now limit libci tests to be GHA-specific
• allow 3x timeout waiting for dds devices under GHA
• give dds test-librs-device-properties context a name
• fix dds query_devices: discard non-running devices; now product-line sensitive