When executing `make test` on devices using JLink, testrunner
launches `make term` which calls `jlink.sh term_rtt`. When finished
the father process is killed but `setsid` has launched JLinkExe
as another subprocess, which is not killed by `os.killpg` from
testrunner since it doesn't belong to the same group.
While running `make term` JLinkExe is expecting commands and thus
can be disturbed by other JLink commands, e.g. `make reset`.
This enable `make test` (which runs those two commands at the same
time) on target using JLinkExe as a programmer/debugger.
