Split migration config to separate file

This patch splits the migration configuration information into a separate file.

It also adds a paragraph about volume-backed live migration w/o shared storage,
a feature that was added in grizzly

Fix build.

patchset 3 rebases.

patchset 4 rebases

patchset 5 fixes xml syntax

fixes bug 1087050
bp:restructure-documentation

Change-Id: I608a0be61a886ea1239b9e184d5e4bd70acd63c8
Merge "Split migration config to separate file"