update public CI so we run tests on same combinations of python+docker

Signed-off-by: Nicolas De Loof <[email protected]>

Jenkinsfile

@@ -1,8 +1,8 @@
 #!groovy
 
-def dockerVersions = ['19.03.5', '18.09.9']
+def dockerVersions = ['19.03.5']
 def baseImages = ['alpine', 'debian']
-def pythonVersions = ['py27', 'py37']
+def pythonVersions = ['py37']
 
 pipeline {
     agent none