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).
Merge pull request #1223 from deis/fix_component_rsync

fix(Makefile): fix component rsync