Generate certificates out of band

In order to fully test TLS client authentication, CA infrastructure is
needed. This is generated by https://github.com/iSECPartners/tlspretense

Ultimately, these certificates will be generated in-band via
TLSPretense, once there is a solution to
https://github.com/iSECPartners/tlspretense/issues/3.
Adds support for setting a custom truststore

Adds support for setting a custom truststore that will be applied to any
SSL connections created by this client.
Adds support for setting a custom keystore

This enables TLS client authentication