add contrib/jenkins.sh from current jenkins.osmocom.org job

i.e. from https://jenkins.osmocom.org/jenkins/job/update-osmocom-python-on-slaves

Change-Id: Iefa0261303982fc66d0845348b9c4a0ff6b94ab5
diff --git a/contrib/jenkins.sh b/contrib/jenkins.sh
new file mode 100755
index 0000000..802ba2d
--- /dev/null
+++ b/contrib/jenkins.sh
@@ -0,0 +1,4 @@
+#!/bin/sh
+python2 ./setup.py install || python ./setup.py install
+rm -rf ./build
+python3 ./setup.py install