Pin sh library used for molecule tests

This pin works for python2 and python3 environments
and resolves:

ansible/molecule#2676

We unfortunately have molecule pinned, so we won't
inherit any fixes (including this one) from newer
releases.

Change-Id: Ia29419966efcadb1c996f7f5785354698ecc80c3
(cherry picked from commit 3c47a46)

molecule/molecule-requirements.txt

@@ -7,5 +7,6 @@ pytest-cov
 pytest-html
 pytest-xdist
 mock
+sh>=1.12.14,<1.13
 molecule>=2.22rc1,<3
 netaddr