Expands the Boot from Volume documentation.

This commit adds some further information about booting from volumes. It
ensures the features are updated for Grizzly. Also removes a duplicate
section about booting from volumes. Also updates the Ops Guide with this
info.

Change-Id: Iac6a4caa36da388936543c7a3aaed3af1429bdd0
Fixes: bug #1163580