(PUP-1527) After upgrade from 3.3.2-1 to 3.4.2-1 naginator fails to
create config from exported resources taken from hiera

Some changes introduced in hiera around 3.4 resulted in type coersion
from strings to FixNums when creating exported resources that were
partially built from hiera data.

This patch ensures that any non-array parameter passed through the
Nagios::Base.to_s is actually a string before trying to run the .sub
method on it, and so fixes the above error with exported resources
whilst also introducing support for fixnum params for any of the nagios
type parameters