fix(Makefile): fix component rsync

Currently, trying to issue a `make -C <component> build` will rsync
the contents of that component directory to /home/core/share instead
of /home/core/share/<component>.

This commit makes all rsync commands rsync relative to the root directory
(using the path to includes.mk as a reference).
feat(*): allow custom component images

Pull image names for Deis components from etcd, defaulting to the
stock Deis component images. This enables users to supply their own
router, for instance, simply by setting an etcd key:

/deis/{component}/image

Also, the Deis release version is now stored in /etc/deis-release.
This is by default appended when getting the image names for Deis
components, but can be overridden if set in etcd at /deis/release.
feat(*): move data containers into new unit files

Moving these containers into their own data files
sets the stage for locking data containers to specific
machines. This also enables us to stop Postgres cleanly on
the database-data container.

closes #638
fix(*): schedule data containers to specific machines

Currently, whenever database, logger, registry, or builder are rescheduled
by fleet, their data container is left on the original machine. The effect
for the user is that they lose their data! This commit schedules data containers
to a preselected machine. If that machine goes down, the underlying service will
go down, but this is preferred to scheduling it on another host that won't have
the data.

Note that this is an interim fix - stateful data should be stored off-host.

closes #1038
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