Use pattern matching over asInstanceOf in test

A safer alternative (although we still throw in the default case).

Change-Id: I961f02ec82e7b6dc84d24d235be0d2d9111657c6

src/test/scala/com/googlesource/gerrit/plugins/analytics/test/GerritTestDaemon.scala

diff --git a/src/test/scala/com/googlesource/gerrit/plugins/analytics/test/GerritTestDaemon.scala b/src/test/scala/com/googlesource/gerrit/plugins/analytics/test/GerritTestDaemon.scala
index dd79434..bfd5a20 100644
--- a/src/test/scala/com/googlesource/gerrit/plugins/analytics/test/GerritTestDaemon.scala
+++ b/src/test/scala/com/googlesource/gerrit/plugins/analytics/test/GerritTestDaemon.scala
@@ -161,7 +161,10 @@
   }
 
   def getRepository(projectName: Project.NameKey): FileRepository =
-    repoManager.openRepository(projectName).asInstanceOf[FileRepository]
+    repoManager.openRepository(projectName) match {
+      case repository: FileRepository => repository
+      case repository => throw new IllegalStateException(s"Expected 'FileRepository', got ${repository.getClass.getName}")
+    }
 
   def adminAuthor = admin.newIdent