(PUP-1527) After upgrade from 3.3.2-1 to 3.4.2-1 naginator fails to crea...

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 coercion 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 
method is a string before trying to run the .sub method on it.
RSpec expectations that a given error will not be raised are deprecated in 2.14; I pulled this down locally and ran the specs and got this:

```
Nagios generator
  should escape ';'
  should escape ';' if it is not already the case
  should be idempotent
DEPRECATION: `expect { }.not_to raise_error(SpecificErrorClass, message)` is deprecated. Use `expect { }.not_to raise_error` (with no args) instead. Called from /home/adrien/eng/projects/platform/puppet/spec/unit/type/nagios_spec.rb:226:in `block (2 levels) in <top (required)>'.
  should not raise a NoMethodError: 'undefined method `sub' for 3:Fixnum when given a FixNum param
  should accept FixNum params and convert to string
```

Expectations like this can capture many other errors, such as `ArgumentError` and other legitimate failures.

The actual test case that we're interested in is the following test; that is a positive that makes sure that the expected behavior happens. If that test fails then this test will fail as well, and if the next test doesn't fail then this can't fail either. Because of this we can probably omit this test.