Update set_seclabel use list in svirt test cases

Using list as given parameter according to vm_xml module change.

Signed-off-by: Wayne Sun <gsun@redhat.com>
svirt_start_destroy: Add cases for multiple seclabels

Add cases for contain both dac and selinux model seclabels, also
with setting in qemu.conf.

Signed-off-by: Wayne Sun <gsun@redhat.com>
svirt_start_destroy: Add cases for security_default_confined as 0

Add unconfined cases with security_default_confined as 0 in qemu.conf

Signed-off-by: Wayne Sun <gsun@redhat.com>
svirt_start_destroy: Add negative cases for security_require_confined as 1

When security_require_confined set as 1, VM with seclabel type as None
will fail to start.

Signed-off-by: Wayne Sun <gsun@redhat.com>
svirt_start_destroy: simplify qemu conf setting code

Signed-off-by: Wayne Sun <gsun@redhat.com>
svirt_start_destroy: Use attr function when set qemu conf

The set_string function is for set string value with quote mark
in conf, which with customize result to avoid raw string in config
file.

For security_driver in qemu conf, set string other than default
list as testing use string.

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