svirt_start_destroy: Add cases for check vm process CAP_SYS_RAWIO capability

Set vm process use 'root' to start, then attach iscsi and disk pool vol,
check the vm process has CAP_SYS_RAWIO capability.

This test case is come from bug:
https://bugzilla.redhat.com/show_bug.cgi?id=767425

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