Verify if imagename and tagname params are not empty

[aadeshpa]

/bin/bash: line 14: params.docker-imagename: command not found
/bin/bash: line 14: params.docker-imagetag: command not found
[INFO] Stack registry URL = docker.io
[INFO] Application image URL = image-registry.openshift-image-registry.svc:5000/kabanero/-t
[INFO] Running appsody build...
[Warning]
*

When you do not provide the imagename and the tagname while running the pipelinerun manually you will get above error while calling the /scripts/imageurl_imagename_lowercase.sh and it cause the above issue of Application image URL to be malformed.

[aadeshpa]

The PR fix for this issue is : #389