dumpxml: Add acl test cases for domain api read and read-secure

By default access with domain api 'read' will be granted
for unprivileged user, add test cases testing this via
dumpxml command.

And for dumpxml with --security-info, add test cases with
domain api 'read-secure' in normal and error tests.

Signed-off-by: Wayne Sun <gsun@redhat.com>
Merge pull request #335 from waynesun09/acl_dumpxml

dumpxml: Add acl test cases for domain api read and read-secure