selftests/resctrl: Simplify cleanup in ctrl-c handler

selftests/resctrl: Simplify cleanup in ctrl-c handler

Ctrl-c handler isn't aware of what test is currently running. Because of
that it executes all cleanups even if they aren't necessary. Since the
ctrl-c handler uses the sa_sigaction system no parameters can be passed
to it as function arguments.

Add a global variable to make ctrl-c handler aware of the currently run
test and only execute the correct cleanup callback.

Signed-off-by: Maciej Wieczor-Retman <maciej.wieczor-retman@intel.com>
Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>