tests: add optional output for Python 2.7 deprecation

We already had one of these a few lines above. We need it here as
well.

Differential Revision: https://phab.mercurial-scm.org/D6203

tests/test-install.t

@@ -242,6 +242,7 b' the default for them.'
 Note: we use this weird path to run pip and hg to avoid platform differences,
 since it's bin on most platforms but Scripts on Windows.
   $ ./installenv/*/pip install --no-index $TESTDIR/.. >> pip.log
+  DEPRECATION: Python 2.7 will reach the end of its life on January 1st, 2020. Please upgrade your Python as Python 2.7 won't be maintained after that date. A future version of pip will drop support for Python 2.7. (?)
   $ ./installenv/*/hg debuginstall || cat pip.log
   checking encoding (ascii)...
   checking Python executable (*) (glob)