apparmor: allow qemu abstraction to read /proc/pid/cmdline
Noticed the following denial in audit.log when shutting down
an apparmor confined domain
type=AVC msg=audit(1512002299.742:131): apparmor="DENIED"
operation="open" profile="libvirt-66154842-e926-4f92-92f0-1c1bf61dd1ff"
name="/proc/1475/cmdline" pid=2958 comm="qemu-system-x86"
requested_mask="r" denied_mask="r" fsuid=469 ouid=0
Squelch the denial by allowing read access to /proc/<pid>/cmdline.