Make '--app' and '--compiler' explicit in run_on_app.py

Also fix d8.py not printing the d8 command line.

Bug:
Change-Id: Ice2fb5f8c50c85e1cd820a258d3a985792953dd7
diff --git a/tools/d8.py b/tools/d8.py
index cb0c841..d214cf5 100755
--- a/tools/d8.py
+++ b/tools/d8.py
@@ -24,6 +24,7 @@
     cmd.append('-agentlib:hprof=cpu=samples,interval=1,depth=8')
   cmd.extend(['-jar', D8_JAR])
   cmd.extend(args)
+  utils.PrintCmd(cmd)
   subprocess.check_call(cmd)
 
 def main():