Defer requirement of securerandom, use regular require

[djberg96]

Since #218 we've been seeing this warning in the console and/or rails logs:

securerandom.rb:275: warning: already initialized constant Random::Formatter::ALPHANUMERIC
securerandom.rb:275: warning: previous definition of ALPHANUMERIC was here

This appears to be caused by load-ing securerandom after it's already been require'd somewhere else.

I'm not sure why it was written this way since securerandom should already be loaded (via rails, in active_support.rb, among other places). Since it's only used within a single method, I've moved it into that method so that it's deferred until needed, and changed it to a regular require. The specs still seem to pass.

[djberg96]

@miq-bot add_label refactoring

[miq-bot]

Checked commits https://github.com/djberg96/manageiq-providers-vmware/compare/a6b665e93628e808dcebdd8d82d5b3ab54d430e6~...04ce352a911d8d3797969a713645bf226e5f14d8 with ruby 2.5.5, rubocop 0.69.0, haml-lint 0.20.0, and yamllint 1.10.0
2 files checked, 0 offenses detected
Everything looks fine. 🍪