Events reported by forked tests should be sequence of (String, SuiteResult)

Currently events reported by forked tests are a `Map[String, SuiteResult]`. With some configurations (in particular, nested suites in ScalaTest), the suite name is the same for all nested suites. Using a Map causes loss of reporting information for all but one tests with the same name.

Changing this to a Seq allows all results to be reported.

This is related to https://github.com/scalatest/scalatest/issues/167
Also related to https://github.com/sbt/sbt/pull/1364
But this fixes the issue when `fork in Test := true`.

Example failure at https://gist.github.com/fiadliel/4071e61b3fd9331a81d4