Don't use other params in param default

[llowder]

With newer(ish) puppet, you cannot use a class/define param as part of the default value for another param.

Using OS puppet 4.5.3 with version 0.1.4 of this module, we ran into the following:

In a wrapper class, we set a value for shibboleth::metadata::provider_uri and shibboleth::metadata::cert_uri then called shibboleth::metadata with default values for the rest of the params.

The puppet run then fails with the following:

Could not retrieve catalog from remote server: Error 400 on SERVER: 
Evaluation Error: Error while evaluating a Resource Statement, 
Evaluation Error: Error while evaluating a Function Call, Failed to parse inline template: 
Undefined method 'split' for nil:NilClass at <location>/shibboleth/manifests/metadata.pp:7:31 
at <wrapper class location> 
on <node>

See this issue and the ones listed as "relates to" for additional information: https://tickets.puppetlabs.com/browse/PUP-1080