selftests/livepatch: push and pop dynamic debug config

The livepatching self-tests tweak the dynamic debug config to verify
the kernel log during the tests.  Enhance set_dynamic_debug() so that
the config changes are restored when the script exits.

Note this functionality needs to keep in sync with:
  - dynamic_debug input/output formatting
  - functions affected by set_dynamic_debug()

  For example, push_dynamic_debug() transforms:
    kernel/livepatch/transition.c:530 [livepatch]klp_init_transition =_ "'%s': initializing %s transition\012"
  to the following:
    file kernel/livepatch/transition.c line 530 =_

Signed-off-by: Joe Lawrence <joe.lawrence@redhat.com>
Tested-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>