build: Install bash completions below DESTDIR
build: Install bash completions below DESTDIR

Honour the DESTDIR variable when installing the bash completion script.

Fixes #566.

Signed-off-by: James O. D. Hunt <348fbaadfbada55ea105602bf5609e23ac1c4898@intel.com>

chavafg/runtime,devimc/runtime,clearcontainers/runtime,chavafg/runtime,devimc/runtime,clearcontainers/runtime