Migrate finagle-thrift/finagle-stream tests to ScalaTest

In preparation for 2.11.x finagle-thrift tests will migrate to ScalaTest


Remaining Work:
1) Finagle-Streams
2) 2.11.x testing
3) Conversation about FinagleClientThriftServerSpec structure
4) Renaming tests from *Spec -> *Test
5) Clean up commit history and conform to commit message standards
I don't love the style of OneInstancePerTest, it's not particularly idiomatic scalatest.  Generally we just make a context class and import its contents in each test.  By sticking to one style, it's easier for us to reason about different tests, and by having tightly scoped context classes, we can have more sophisticated fixtures if we have a big test suite, for example.