buildrpm: bump bundled Python version to 2.7.16 when building for centos{5,6} stable

buildrpm: bump bundled Python version to 2.7.16 when building for centos{5,6}

When building rpm packages for centos 5 and 6, we bundle a mercurial-specific
version of Python 2.7 in /opt/python-hg.

This change is analogous to 5e947367606c, and bumps the embedded Python version
from 2.7.14 (released in 2017) to 2.7.16 (latest as of today).

--- a/contrib/Makefile.python	Sun Apr 21 08:57:01 2019 -0700
+++ b/contrib/Makefile.python	Fri Apr 19 02:24:25 2019 +0200
@@ -1,4 +1,4 @@
-PYTHONVER=2.7.14
+PYTHONVER=2.7.16
 PYTHONNAME=python-
 PREFIX=$(HOME)/bin/prefix-$(PYTHONNAME)$(PYTHONVER)
 SYMLINKDIR=$(HOME)/bin

--- a/contrib/packaging/buildrpm	Sun Apr 21 08:57:01 2019 -0700
+++ b/contrib/packaging/buildrpm	Fri Apr 19 02:24:25 2019 +0200
@@ -20,8 +20,8 @@
         ;;
     --withpython | --with-python)
         shift
-        PYTHONVER=2.7.14
-        PYTHONMD5=cee2e4b33ad3750da77b2e85f2f8b724
+        PYTHONVER=2.7.16
+        PYTHONMD5=f1a2ace631068444831d01485466ece0
         ;;
     --rpmbuilddir )
         shift