software/slapos-testing: extend stack/caucase to get versions from there

Instead of duplicating the versions and having an old pin to a version
which is now older than caucase minimum required version.

software/slapos-testing/software.cfg

@@ -14,6 +14,7 @@ extends =
   ../../component/lmsensors/buildout.cfg
   ../../component/rsync/buildout.cfg
   ../../stack/slapos.cfg
+  ../../stack/caucase/buildout.cfg
   ../../stack/nxdtest.cfg
   ./buildout.hash.cfg
 
@@ -235,12 +236,8 @@ httmock = 1.2.6
 manuel = 1.9.0
 mock = 2.0.0
 testfixtures = 6.11.0
-pem = 18.1.0
 pycurl = 7.43.0.2
 pyflakes = 2.0.0
 zope.testing = 4.6.2
 urllib3 = 1.24.1
 pathlib = 1.0.1
-# Required by:
-# caucase
-PyJWT = 1.6.4