Description of problem:
User can setup ganesha without having any volumes and later they can create and export volumes. Hence, volname should be made optional in nfs-ganesha create-cluster.

Version-Release number of selected component (if applicable):
gdeploy-2.0.1-3.el7rhgs.noarch

How reproducible:
Always

Steps to Reproduce:
1. Create nfs.ganesha.conf without 'volname' key in create-cluster.
2. Run gdeploy for setting up ganesha.

Actual results:
Ganesha cluster creation succeeds, but it also tries to export volume which is undefined in conf file and it fails.

Expected results:
Ganesha cluster creation should succeed without any error.

Additional info:

Error Message:

TASK [Exports/Unexports volume through NFS-Ganesha] ****************************
fatal: [dhcp46-111.lab.eng.blr.redhat.com]: FAILED! => {"failed": true, "msg": "the field 'args' has an invalid value, which appears to include a variable that is undefined. The error was: 'volname' is undefined\n\nThe error appears to have been in '/tmp/tmpI5Ra8w/gluster-volume-export-ganesha.yml': line 7, column 7, but may\nbe elsewhere in the file depending on the exact syntax problem.\n\nThe offending line appears to be:\n\n  tasks:\n    - name: Exports/Unexports volume through NFS-Ganesha\n      ^ here\n"}
to retry, use:
                --limit
                @/tmp/tmpI5Ra8w/gluster-volume-export-ganesha.retry