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).