Clarified location of driver config settings; removed ESX driver reference; minor text edits.

UPDATED part 3: Build failed! fixed program listing tags
UPDATED part 2: Build failed. Checked and modified tag formatting.
UPDATED: Removed tabs and applied correct use of <filename> tags.

* Clarified details of volume driver configuration settings for VMDK drivers in nova.conf and cinder.conf.

* Removed reference to ESX/ESXi server driver config because it has not been extensively tested.

* Changed occurrences of "data store" to "datastore" for consistency.

Change-Id: I2a45b131fa19749530f5fe93115518f8b9f4ea4e
backport: havana
Closes-Bug: #1260005
Cleaned up section_compute-configure-backing-storage

Fixed typo, removed "s"
disk should not be plural, changed from disks to disk

Change-Id: I7e0d0fdb89e26f4b3a08a4ab6251476c08220be1
Merge "Clarified location of driver config settings; removed ESX driver reference; minor text edits."