(SERVER-29) exclude BouncyCastle jars from uberjar

Yo dawg, JRuby bundles the BouncyCastle .jars in its .jar.  Avoid using these,
since this project defines its own dependency on BouncyCastle directly.

I tested this by building an uberjar (that includes jetty) and doing an agent run against it.  It worked fine, with no obvious problems.