Description of problem:

grafton-sanity-check doesn't fail when a given disk doesn't exist or disk is not empty

Version-Release number of selected component (if applicable):
gdeploy-2.0.1-11.el7rhgs

How reproducible:
Always

Steps to Reproduce:
1. Create gdeploy configuration file like the following.
##################################################################
[hosts]
dhcp42-123.lab.eng.blr.redhat.com
dhcp43-152.lab.eng.blr.redhat.com

[script1]
action=execute
ignore_script_errors=no
file=/usr/share/ansible/gdeploy/scripts/grafton-sanity-check.sh -d vdb,xxx -h dhcp42-123.lab.eng.blr.redhat.com,dhcp43-152.lab.eng.blr.redhat.com
########################################################################

2. Give a disk name which does not exists and another disk name which is already used (Either as OS partition or as Gluster Brick)

  In the above example, disk 'vdb' is used already used for OS installation and disk 'xxx' doesn't exists in any system.

Actual results:
[root@dhcp42-123 ~]# echo $?
0
[root@dhcp42-123 ~]# 


grafton-sanity-check.sh passes and return success code 0. 


Expected results:

grafton-sanity-check.sh should fail to indicate that disk xxx doesn't exist and disk 'vdb' is not blank.