Resync stable charm-helpers to pickup fstab fix
Sync charm-helpers from lp:charm-helpers
Resync stable helpers
[jamespage, r=gnuoy] Stable update for fstab persistence
[gnuoy, r=tribaal] Sync charm-helpers from lp:charm-helpers
- Please see https://bugs.launchpad.net/charms/+source/swift-storage/+bug/1276911 comment #8
	- There is a divergence between the changes made by me ( lp:~niedbalski/charms/precise/swift-storage/add-fstab-persist) and the changes proposed on lp:~james-page/charms/trusty/swift-storage/fstab-persist.
Merging changes from lp:~niedbalski/charms/trusty/swift-storage/mr-corrected-1276911