Pin the libjuju version

There is a pending release of libjuju that will break compatibility with
the version we're currently using. This won't be a problem when we
switch to using the version within N2VC, but there's more work involved
with that.

This patch just installs the specific version we've been using, 0.6.1,
so that new installs won't get the new version.

Signed-off-by: Adam Israel <adam.israel@canonical.com>
diff --git a/jenkins/SO/install b/jenkins/SO/install
index 7000c8e..9cad24a 100755
--- a/jenkins/SO/install
+++ b/jenkins/SO/install
@@ -140,4 +140,4 @@
 # Install libjuju
 apt-get install -y python3-pip python3-setuptools
 
-pip3 install juju
+pip3 install juju==0.6.1