Add support for reboot into API

[pevik]

Support for reboot in LTP tests would be useful for certain tests. Based on original proposal from Cyril.

Adding reboots_machine flag to the tst_test structure, which will inform the test framework that the test will reboot the machine in the middle of the test.

• The framework will have to inevitably run on a different machine, but the runltp-ng already does that.

• The framework will reconnect to the machine after a reboot and re-execute the test with a flag that would say that this is a second stage of the test, i.e. after reboot.

  Blocker for this is to integrate runltp-ng into LTP (some issues are pending, at least timeout issue: https://github.com/metan-ucw/runltp-ng/issues/31 https://patchwork.ozlabs.org/project/ltp/list/?series=247935 and better taint flag handling https://github.com/metan-ucw/runltp-ng/issues/40).

See also blog post Towards parallel kernel test runs.

[metan-ucw]

@acerv FYI this is something that should go into the new testrunner later on.