qemu-ga: use state dir from CONFIG_QEMU_LOCALSTATEDIR

qemu-ga: use state dir from CONFIG_QEMU_LOCALSTATEDIR

Has the side effect of changing the default directory used to
save the freeze status file from /tmp to ${prefix}/var/run.

This is a beneficial change for two reasons:

  1. FHS states that programs must not assume that files in /tmp will
     still exist between invocations of the program. This defeats
	 the purpose of the freeze status file

  2. FHS dictates that /var/run must be cleaned on boot, this
     ensures that a stale freeze status file will be removed on boot

Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Michael Roth <mdroth@linux.vnet.ibm.com>
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>