Get BINFILE and ELFFILE from command line instead of environment variable.
Rename 'HEXFILE' to 'BINFILE' in the script as the binary file is used.
The documentation was already talking about 'BINFILE' but 'BINFILE'
was never exported by the build system and it was using 'HEXFILE' in the
implementation.
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.
