Enable Scala 2.11 SBT builds for util-eval, ostrich, and finagle-ostrich4

Problem

We want to publish 2.11 releases of Finagle subprojects that depend on Ostrich,
which we have not previously built for 2.11 (because it has specs tests, and
because it depends on scala-json and util-eval, neither of which previously
worked on 2.11).

Solution

util-eval previously didn't work on 2.11 because `scala.ScalaObject` has been
removed since 2.10. This is fixed here. The bulk of this commit is Rodrigo
Lazoti's migration of Ostrich's tests from specs to ScalaTest (I'm not using his
pull request since the PR also replaces scala-json with Jackson, which we don't
want to do at this time to avoid breaking public APIs). This commit also
reinstates util-eval and the Finagle subprojects that depend on Ostrich in their
projects' cross-builds.

Result

util-eval, ostrich, finagle-ostrich4, finagle-example, and finagle-stress all
build and pass tests on 2.11 (from SBT) for the first time.

RB_ID=534127