fix: Update Ansible pip package to '2.5.5' (IBM#163)

Ansible version '2.5.2' has a bug that will display "[ERROR]:" when
running a dynamic inventory script
(ansible/ansible#39007) due to an appended new
line character. This issue is resolved by
ansible/ansible#39019 which is included in
Ansible version '2.5.5'.

scripts/venv_install.sh

@@ -19,7 +19,7 @@ sudo -E -H pip install --upgrade virtualenv
 virtualenv --no-wheel --system-site-packages ${1}pup-venv
 source ${1}pup-venv/bin/activate
 pip install \
-    'ansible==2.5.2' \
+    'ansible==2.5.5' \
     'orderedattrdict==1.5' \
     'pyroute2==0.5.0' \
     'jsonschema==2.6.0' \