kunit: Introduce autorun option

The new option controls tests run on boot or module load. With the new
debugfs "run" dentry allowing to run tests on demand, an ability to disable
automatic tests run becomes a useful option in case of intrusive tests.

The option is set to true by default to preserve the existent behavior. It
can be overridden by either the corresponding module option or by the
corresponding config build option.

Link: https://lore.kernel.org/r/173015245931.4747.16419517391658830640.stgit@skinsburskii-cloud-desktop.internal.cloudapp.net


Signed-off-by: Stanislav Kinsburskii <skinsburskii@linux.microsoft.com>
Reviewed-by: Rae Moar <rmoar@google.com>
Acked-by: David Gow <davidgow@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>