Fix baremetal flavor image size

When storing the node details in the JSON datafile, the DISK size
was incremented for baremetal nodes creation and store after that,
so the baremetal flavor was created with a root disk size bigger
than expected.

Closes-Bug: #1290399
Change-Id: Idc6a3d4f89badeeffb2e17ac84e10cbfa3629de6
Merge "Fix baremetal flavor image size"