Test whether sample config generation works

Test whether sample config generation works

Adds --checkonly to tools/config/check_uptodate.sh.

This allows verifying that a configuration file was
generated.

We have had a number of issues introduced which
have caused config file generation to fail since we
removed the sample config file check in the gate.
This does not add back checks to ensure that the file
has been updated, it only checks to ensure that it is
still possible to update the sample file.

Change-Id: I2e0e376fbdec5a1bb584c6739231649e1d0f5d8e