Fix the pid_mode and ipc_mode value check for kolla_docker module

bypass_checks is disabled by Ib2e19794bbe804470a880253d5870254041358c8 .
But we use pid_mode: "{{ service.pid_mode | default('') }}" pattern in
the yaml file. whereas pid_mode only support "host" value, this patch
add '' as a choice of these two parameters.

Change-Id: Ib83ed5e437ca868f0e42ce740ad1125d2fa48ff4