fix 1138 installing cryptography>=2.5 with pip

Change-Id: I8b1f0481cafdc045483876aa4e956f81e23f8bbe
Signed-off-by: tierno <alfonso.tiernosepulveda@telefonica.com>
diff --git a/docker/RO/Dockerfile b/docker/RO/Dockerfile
index 4107b48..299fbbe 100644
--- a/docker/RO/Dockerfile
+++ b/docker/RO/Dockerfile
@@ -47,6 +47,8 @@
     python3-osm-rovim-openstack${RO_VERSION} python3-osm-rovim-openvim${RO_VERSION} \
     python3-osm-rovim-vmware${RO_VERSION}
 
+# ensure right version is installed as pyhton3-ccryptography install an old version
+RUN python3 -m pip install --upgrade "cryptography>=2.5"
 
 VOLUME /var/log/osm