Use the "swiss army knife" jar for all tools except r8lib-de and r8lib-r8

The toolhelper.py support other tools than 'r8', 'd8', 'r8lib-d8' and
'r8lib-r8', e.g. 'disasm'.

Change-Id: I8fe7c4329e24eb0459ab0bc249569d5dda0476cb
diff --git a/tools/toolhelper.py b/tools/toolhelper.py
index d9c96f1..532af6d 100644
--- a/tools/toolhelper.py
+++ b/tools/toolhelper.py
@@ -24,13 +24,12 @@
     cmd.append('-ea')
   if profile:
     cmd.append('-agentlib:hprof=cpu=samples,interval=1,depth=8')
-  if tool in ['r8', 'd8']:
-    cmd.extend(['-jar', utils.R8_JAR, tool])
+  if tool == 'r8lib-d8':
+    cmd.extend(['-cp', utils.R8LIB_JAR, 'com.android.tools.r8.D8'])
   elif tool == 'r8lib-r8':
     cmd.extend(['-cp', utils.R8LIB_JAR, 'com.android.tools.r8.R8'])
   else:
-    assert(tool == 'r8lib-d8')
-    cmd.extend(['-cp', utils.R8LIB_JAR, 'com.android.tools.r8.D8'])
+    cmd.extend(['-jar', utils.R8_JAR, tool])
   lib, args = extract_lib_from_args(args)
   if lib:
     cmd.extend(["--lib", lib])