Allow passing in timeout/retry settings to Net::HTTP

[johnnyshields]

Replaces #677

Allow passing in Net::HTTP :open_timeout, :read_timeout, and :max_retries settings to IdpMetadataParser#parse_remote.

When fetching remote XML files from arbitrary URLs, you might want to configure different values for timeouts/retries to avoid allowing users to DoS you via intentionally slow endpoints. The Net::HTTP defaults are 60 seconds plus 1 retry, which could easily deplete resources if intentionally exploited.

I also added some additional test coverage for IdpMetadataParser#parse_remote_to_array which was missing.