Allow DER certificates to be converted to PEM format

[n3mawashi]

Augments the openssl::export::pem_cert code to test on DER certificates. Change der_cert and pfx_cert to optional to allow the removal of cert to succeed. There is a unit test to confirm all functionality

[puppet-community-rangefinder]

openssl::export::pem_cert is a type

that may have no external impact to Forge modules.

openssl::export::pem_key is a type

that may have no external impact to Forge modules.

This module is declared in 2 of 576 indexed public Puppetfiles.

---

These results were generated with Rangefinder, a tool that helps predict the downstream impact of breaking changes to elements used in Puppet modules. You can run this on the command line to get a full report.

Exact matches are those that we can positively identify via namespace and the declaring modules' metadata. Non-namespaced items, such as Puppet 3.x functions, will always be reported as near matches only.

[raphink]

Thanks for that. I've added a few comments.

[raphink]

Sorry, my bad. Linting issues ;-)