Few flashers require a longer time to flash code and reset the device and
requires the test script to wait for a longer time before timing out.
This commit adds a environment variable "RIOT_TEST_TIMEOUT" that can be
set by the user to vary the timeout in accordance to the requirements
of the system
on-behalf-of: @sparkmeter <sanju.kannioth@sparkmeter.io>
I had this idea when implementing #10382 and #10392 as I introduced a
very similar structure to python's standard unittests in those and it
could also reduce some code duplication between those two tests.
If not defined it was raising a KeyError. Use the 'get' function to
handle non defined value.
It did not put the value in the `default` case as it would have changed
the behavior when `RIOTBASE` is defined but empty.
