Changes

debian: build armv6 binaries for armhf

Debian armhf is armv7 and hard-float, and Raspbian is a rebuild of
Debian with armv6 and hard-float. This is done to make use of the
BCM2835 FPU, as while the Debian armel (armv5 and soft-float) port
works, it does not make full use of the CPU's hardware.

By making this change, our 'armhf' binaries will work on both armv6 and
armv7 systems.

Signed-off-by: Bjorn Neergaard <bjorn.neergaard@docker.com>