selftests/kselftest/runner.sh: Pass optional command parameters in environment

Some testcases allow for optional commandline parameters but as of now
there is now way to provide such arguments to the runner script.

Add support to retrieve such optional command parameters fron environment
variables named so as to include the all-uppercase test executable name,
sanitized substituting any non-acceptable varname characters with "_",
following the pattern:

	KSELFTEST_<UPPERCASE_SANITIZED_TEST_NAME>_ARGS="options"

Optional command parameters support is not available if 'tr' is not
installed on the test system.

Cc: Kees Cook <keescook@chromium.org>
Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>