[tmp] fixup OpenSSL for Python2 SRs

This commit is kept separate on purpose until nexedi/master is stable.

stack/slapos-py2.cfg

@@ -4,6 +4,9 @@ extends = slapos.cfg
 [python]
 part = python2.7
 
+[openssl]
+<= openssl-1.1
+
 # Use Python2-compatible versions of zc.buildout dependencies from the start.
 # These versions must be pinned unconditionally because slapos.rebootstrap
 # will necessarily keep the same versions of zc.buildout and dependencies