apparmor, libvirt-qemu: add default pki path of libvirt-spice

apparmor, libvirt-qemu: add default pki path of libvirt-spice

Adding the PKI path that is used as default suggestion in src/qemu/qemu.conf
If people use non-default paths they should use local overrides but the
suggested defaults we should open up.

This is the default path as referenced by src/qemu/qemu.conf in libvirt.

While doing so merge the several places we have to cover PKI access into
one.

Bug-Ubuntu: https://bugs.launchpad.net/bugs/1690140

Signed-off-by: Christian Ehrhardt <christian.ehrhardt@canonical.com>