Do not use qemu-img --backing-chain or --output=json

Initial code for GlusterFS snapshot support in Havana
used qemu-img arguments which are too new to run in many
environments.  Run qemu-img using only arguments which
will exist on older platforms.

Partial-Bug: #1224030
Change-Id: I5155dac492da67a951ede978c2c46a54c239eb04