tests: domcaps: Add a default 'empty' test

The 'empty' demonstrates XML generated when only bare minimum caps
data has been filled in. This will demonstrate changes that alter
the default XML output.
Acked-by: NMichal Privoznik <mprivozn@redhat.com>
Signed-off-by: NCole Robinson <crobinso@redhat.com>

tests/domaincapsschemadata/empty.xml

+<domainCapabilities>
+  <path>/bin/emulatorbin</path>
+  <domain>kvm</domain>
+  <machine>my-machine-type</machine>
+  <arch>x86_64</arch>
+  <iothreads supported='no'/>
+  <os supported='no'/>
+  <cpu>
+    <mode name='host-passthrough' supported='no'/>
+    <mode name='host-model' supported='no'/>
+    <mode name='custom' supported='no'/>
+  </cpu>
+  <devices>
+    <disk supported='no'/>
+    <graphics supported='no'/>
+    <video supported='no'/>
+    <hostdev supported='no'/>
+  </devices>
+  <features>
+    <gic supported='no'/>
+    <vmcoreinfo supported='no'/>
+    <genid supported='no'/>
+    <sev supported='no'/>
+  </features>
+</domainCapabilities>

tests/domaincapstest.c

@@ -433,6 +433,9 @@ mymain(void)
         VIR_FREE(name); \
     } while (0)
 
+    DO_TEST("empty", "/bin/emulatorbin", "my-machine-type",
+            "x86_64", VIR_DOMAIN_VIRT_KVM, CAPS_NONE);
+
 #if WITH_QEMU
 
     DO_TEST_QEMU("1.7.0", "caps_1.7.0",