dac_start_destroy: Add dac test cases

DAC is default enabled security driver in libvirt. In this start
and destroy test, cover per-VM DAC setting, global configuration
in qemu.conf alone testing and mix per-VM and global testing.

Signed-off-by: Wayne Sun <gsun@redhat.com>
dac_start_destroy: Replace qemu conf sync function

The utils_config module updated, the sync function is removed,
update test case to use utils_libvirtd module for restart libvirtd
after conf change.

Signed-off-by: Wayne Sun <gsun@redhat.com>
dac_start_destroy: Add case to cover security_default_confined as 0

Add case for cover unconfined DAC testing, 2 cases added to cover bug:
https://bugzilla.redhat.com/show_bug.cgi?id=1105939

New cases with 'security_default_confined = 0' and seclabel as:
<seclabel type='none' model='dac' relabel='yes'/>

Signed-off-by: Wayne Sun <gsun@redhat.com>