Avoid "volumeMounts" with "configMap" fixed permissions

Avoid "volumeMounts" with "configMap" fixed permissions

To access to the container without using a password, the jumphost
RSA public key is copied to each container, using "volumeMounts"
defined as "configMap", to /root/.ssh/authorized_keys.

To work properly, the following permissions must be set:
  - /root/.ssh: 700
  - /root/.ssh/authorized_keys: 600

Because of [1][2], the mounted folders have fixed permissions and
cannot be modified.

[1]https://groups.google.com/forum/#!topic/kubernetes-dev/eTnfMJSqmaM
[2]https://github.com/kubernetes/kubernetes/issues/28317

JIRA: YARDSTICK-1149

Change-Id: I821064da56699c5b4f509d233c33e55af119fd56
Signed-off-by: Rodolfo Alonso Hernandez <rodolfo.alonso.hernandez@intel.com>