Make check for compilation errors in tools/utils a bit more precise

If one tries to unzip/zip a file with the name AssertionError, the
current check fails.

Change-Id: I0b1f0fb6dba3059251aef6b41270314c70f9b860
diff --git a/tools/utils.py b/tools/utils.py
index 8c37a55..b39a168 100644
--- a/tools/utils.py
+++ b/tools/utils.py
@@ -119,9 +119,9 @@
       logger.log(stripped)
 
       # TODO(christofferqa): r8 should fail with non-zero exit code.
-      if ('AssertionError' in stripped
-          or 'CompilationError' in stripped
-          or 'CompilationFailedException' in stripped
+      if ('AssertionError:' in stripped
+          or 'CompilationError:' in stripped
+          or 'CompilationFailedException:' in stripped
           or 'Compilation failed' in stripped):
         failed = True
     else: