qemuDomainNamespaceSetupDisk: Simplify disk check

Firstly, instead of checking for next->path the
virStorageSourceIsEmpty() function should be used which also
takes disk type into account.
Secondly, not every disk source passed has the correct type set
(due to our laziness). Therefore, instead of checking for
virStorageSourceIsBlockLocal() and also S_ISBLK() the former can
be refined to just virStorageSourceIsLocalStorage().
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>

src/qemu/qemu_domain.c

@@ -7912,7 +7912,8 @@ qemuDomainNamespaceSetupDisk(virQEMUDriverPtr driver,
         return 0;
 
     for (next = src; next; next = next->backingStore) {
-        if (!next->path || !virStorageSourceIsBlockLocal(src)) {
+        if (virStorageSourceIsEmpty(next) ||
+            !virStorageSourceIsLocalStorage(next)) {
             /* Not creating device. Just continue. */
             continue;
         }
@@ -7923,12 +7924,8 @@ qemuDomainNamespaceSetupDisk(virQEMUDriverPtr driver,
             goto cleanup;
         }
 
-        if (!S_ISBLK(sb.st_mode)) {
-            virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
-                           _("Disk source %s must be a block device"),
-                           next->path);
-            goto cleanup;
-        }
+        if (!S_ISBLK(sb.st_mode))
+            continue;
 
         if (qemuDomainAttachDeviceMknod(driver,
                                         vm,