Added package target to generate .deb packages

Added package target to generate .deb packages

I'm just calling the underlying `make rw.package` here.
RIFT_PACKAGE_GENERATOR is the variable that controls which types of
packages are generated.

Version numbering uses git describe, which isn't always accurate, but
seems to be reliable enough inside of a CI build system.

Change-Id: I1f460e66145bb7d62267092a718c738e96863b8a
Signed-off-by: Wesley Hirsch <wesley.hirsch@riftio.com>