If the origin/install-script branch exists, use that in preference

Once merged to master we can remove origin/install-script, but
development is awkward without it.  This commit also makes it
easy to have an arbitrary number of fallbacks.
Switch to using 'rake config_files:convert_init_script'

Rather than reimplement the processing of the ugly file with sed,
we can use the existing rake task for rewriting
config/alert-tracks-debian.ugly.
Fix an undefined variable error

I assume 'skip' must have been an argument to this function
before it was introduced into our repository.
Add a rake task to rewrite the crontab-example file

As suggested by Louise Crow, this new rake task reuses
the convert_ugly function to rewrite the crontab-example
file into a usable crontab file.