Restore generic::upstart_job parameters

The lint of the 'generic' module caused the parameters passed to
generic::upstart_job() to be checked as boolean instead of the string as
they used to be.

The parent call have not been updated and are still passing the boolean
as string which cause the condition to never be matched.

This patch let the define to recognize string and boolean values.

Regression introduced by: 4887dc90
  https://gerrit.wikimedia.org/r/#/c/107037/

Change-Id: I03363419c238b696f83b636dc84a79e6a95436d1