Utilize the openssl module to manage TLS certificate

[nmaludy]

Currently we utilize an exec resource to manage the TLS certificate for StackStorm. Instead we should utilize the OpenSSL module https://forge.puppet.com/camptocamp/openssl .

Also, probably be good to add a $manage_ssl_cert option to the ::st2 class in case someone wants to generate their own cert in their own special way.

[nmaludy]

Currently we generate this using an exec (bad practice) https://github.com/StackStorm/puppet-st2/blob/master/manifests/profile/web.pp#L42-L47