Restructure HA Docs to add Active/Active.

The High Availability documentation is being restructured
to allow for both Active/Passive and Active/Active.  This
commit merely reconstructs the structure; no content has
been added or removed.  That will happen on future commits.
There have, however, been additional files added and linked
in the appropriate places, with "Coming Soon" added for the
currently empty chapters.

bug #1196096
blueprint improve-high-availability-support

Change-Id: Iaea7fb0e41801d25ce293bb22843e116b2e23ef5
Merge "Restructure HA Docs to add Active/Active."