software-slapos-sr-testing: Extend stack/caucase .

This allows factorising its version pins.

software/slapos-sr-testing/software.cfg

@@ -15,6 +15,7 @@ extends =
 
   ../../stack/slapos.cfg
   ../../stack/nxdtest.cfg
+  ../../stack/caucase/buildout.cfg
 
   ./buildout.hash.cfg
 
@@ -314,11 +315,6 @@ selenium = 3.141.0
 # Patched eggs
 PyPDF2 = 1.26.0+SlapOSPatched001
 
-# caucase and its dependencies
-caucase = 0.9.4
-pem = 18.2.0
-PyJWT = 1.6.4
-
 # Django 1.11 is python 2 compatible
 Django = 1.11