Switch mterp to python3.

Test: buildbot-build.sh --target
Change-Id: I887caf29b109457c4fdef267d468dedebd9f7430
diff --git a/runtime/interpreter/mterp/common/gen_setup.py b/runtime/interpreter/mterp/common/gen_setup.py
index f92d5f9..4d18136 100644
--- a/runtime/interpreter/mterp/common/gen_setup.py
+++ b/runtime/interpreter/mterp/common/gen_setup.py
@@ -19,7 +19,7 @@
 # the templated snippets. Those define all the helper functions used below.
 
 import sys, re
-from cStringIO import StringIO
+from io import StringIO
 
 out = StringIO()  # File-like in-memory buffer.
 handler_size_bytes = "MTERP_HANDLER_SIZE"
diff --git a/runtime/interpreter/mterp/gen_mterp.py b/runtime/interpreter/mterp/gen_mterp.py
index 5d25955..b8bc2e6 100755
--- a/runtime/interpreter/mterp/gen_mterp.py
+++ b/runtime/interpreter/mterp/gen_mterp.py
@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 #
 # Copyright (C) 2016 The Android Open Source Project
 #
@@ -15,7 +15,7 @@
 # limitations under the License.
 
 import sys, re, os
-from cStringIO import StringIO
+from io import StringIO
 
 SCRIPT_DIR = os.path.dirname(sys.argv[0])
 # This file is included verbatim at the start of the in-memory python script.
@@ -37,9 +37,8 @@
   opcode_fp.close()
 
   if len(opcodes) != NUM_PACKED_OPCODES:
-    print "ERROR: found %d opcodes in Interp.h (expected %d)" \
-        % (len(opcodes), NUM_PACKED_OPCODES)
-    raise SyntaxError, "bad opcode count"
+    print("ERROR: found ", len(opcodes), " opcodes in Interp.h (expected ", NUM_PACKED_OPCODES, ")")
+    raise SyntaxError("bad opcode count")
   return opcodes
 
 indent_re = re.compile(r"^%( *)")