Reland of Work around simctl error when moving from Xcode 7 to Xcode 8.

testing/iossim/iossim.mm

Index: testing/iossim/iossim.mm
diff --git a/testing/iossim/iossim.mm b/testing/iossim/iossim.mm
index f1f0ca86c6e345b59caad9aa46cbf4d9ef8ead24..ebe6249fae7bba8c9e443c0d41199b80bdf5a02c 100644
--- a/testing/iossim/iossim.mm
+++ b/testing/iossim/iossim.mm
@@ -284,6 +284,16 @@
 }
 
 int main(int argc, char* const argv[]) {
+  // When the last running simulator is from Xcode 7, an Xcode 8 run will yeild
+  // a failure to "unload a stale CoreSimulatorService job" message.  Sending a
+  // hidden simctl to do something simple (list devices) helpfully works around
+  // this issue.
+  XCRunTask* workaround_task = [[[XCRunTask alloc]
+      initWithArguments:@[ @"simctl", @"list", @"-j" ]] autorelease];
+  [workaround_task setStandardOutput:nil];
+  [workaround_task setStandardError:nil];
+  [workaround_task run];
+
   NSString* app_path = nil;
   NSString* xctest_path = nil;
   NSString* cmd_args = nil;