samples: net: sockets: can: Fix the test termination criteria

If enabling CONFIG_POSIX_API, we get three file descriptors open
before any socket descriptors. The sample exit criteria checks
socket 0 and 1 which is no longer a valid one, so change the
check to be either 0 or 3, and 1 or 4 so that the test can be
run in both when POSIX API is enabled or disabled.

Also disable color printing for the test run so that it is
easier to read the output log.

Signed-off-by: Jukka Rissanen <jukka.rissanen@nordicsemi.no>