merge_jars.py: Make the code work on Python 3

So far the gerrit build tool chain works as expected on Python 3. The
only problems that we are running into in merge_jars.py:

* ZipFile.read is returning byte and not string
* dict.iteritems() was removed in Python 3

Luckily, those problems can be easily rectified and code can be adjusted
to be compatible with both Python version 2 and 3.

Bug: Issue 7002
Change-Id: I487253b0e2e6fe4428fe60d57879424f85a198a0

tools/merge_jars.py

@@ -17,7 +17,7 @@ from __future__ import print_function
 import collections
 import sys
 import zipfile
-
+import io
 
 if len(sys.argv) < 3:
   print('usage: %s <out.zip> <in.zip>...' % sys.argv[0], file=sys.stderr)
@@ -39,12 +39,14 @@ try:
             continue
           elif n.startswith(SERVICES):
             # Concatenate all provider configuration files.
-            services[n] += inzip.read(n)
+            myfile = inzip.open(n, 'r')
+            myfile = io.TextIOWrapper(myfile, encoding='iso-8859-1', newline='')
+            services[n] += myfile.read()
             continue
           outzip.writestr(info, inzip.read(n))
           seen.add(n)
 
-    for n, v in services.iteritems():
+    for n, v in services.items():
       outzip.writestr(n, v)
 except Exception as err:
   exit('Failed to merge jars: %s' % err)