Leverage the next keyword from python 2.7

This is literally what the next keyword is for.
https://www.python.org/dev/peps/pep-3114/

Change-Id: I843755910b847737b077ff2361ba3e04409db0f0
diff --git a/repo b/repo
index 7e7f13f..7ffa770 100755
--- a/repo
+++ b/repo
@@ -113,7 +113,7 @@
 S_repo = 'repo'                  # special repo repository
 S_manifests = 'manifests'        # special manifest repository
 REPO_MAIN = S_repo + '/main.py'  # main script
-MIN_PYTHON_VERSION = (2, 6)      # minimum supported python version
+MIN_PYTHON_VERSION = (2, 7)      # minimum supported python version
 GITC_CONFIG_FILE = '/gitc/.config'
 GITC_FS_ROOT_DIR = '/gitc/manifest-rw/'
 
@@ -152,9 +152,12 @@
 # Python version check
 ver = sys.version_info
 if (ver[0], ver[1]) < MIN_PYTHON_VERSION:
-  _print('error: Python version %s unsupported.\n'
-         'Please use Python 2.6 - 2.7 instead.'
-         % sys.version.split(' ')[0], file=sys.stderr)
+  _print('error: Python version {} unsupported.\n'
+         'Please use Python {}.{} instead.'.format(
+             sys.version.split(' ')[0],
+             MIN_PYTHON_VERSION[0],
+             MIN_PYTHON_VERSION[1],
+         ), file=sys.stderr)
   sys.exit(1)
 
 home_dot_repo = os.path.expanduser('~/.repoconfig')
@@ -909,6 +912,6 @@
 if __name__ == '__main__':
   if ver[0] == 3:
     _print('warning: Python 3 support is currently experimental. YMMV.\n'
-           'Please use Python 2.6 - 2.7 instead.',
+           'Please use Python 2.7 instead.',
            file=sys.stderr)
   main(sys.argv[1:])