Change the imagePullPolicy from IfNotPresent to Always in APIcast template

In the current state of the APIcast template, the imagePullPolicy is "IfNotPresent". That may result in an older version of an image than expected when deploying images such as master or nightly.
Changing the policy to "Always" assures that the latest version of the image is used and does not introduce much overhead, as the image is pulled only when a change is detected.

https://github.com/3scale/3scale-amp-openshift-templates/blob/baed04acb897f5d3d25ab5fddb2fcc3778c22a0d/apicast-gateway/apicast.yml#L67