Add a field to struct spdk_nvme_ctrlr_opts that allows the user to
specify a keep alive timeout, and add automatic submission of Keep Alive
commands to spdk_nvme_ctrlr_process_admin_completions().
Change-Id: Ib282299a571d8edc59c7933418751bc3a6c98b40
Signed-off-by: Daniel Verkamp <daniel.verkamp@intel.com>