Made Swift backing disk persistent

Previously, Swift's backing disk were not be mounted after reboots,
causing swift-proxy-server service to fail with cryptic error
messages such as 'proxy-server: ERROR Insufficient Storage'. Now,
we use 	Dan Smith' create_disk function from functions to create
the backing disk for us and add it to /etc/fstab.

Change-Id: I9cbccc87bc94a55b58e9badf3fdb127d6f1cf599
1 file changed