qemu: Don't give up on first error in qemuMigrationCancelDriverMirror

When cancelling drive mirror, always try to do that for all disks even
if it fails for some of them. Report the first error we saw.
Signed-off-by: NJiri Denemark <jdenemar@redhat.com>

src/qemu/qemu_migration.c

@@ -1862,6 +1862,8 @@ static int
 qemuMigrationCancelDriveMirror(virQEMUDriverPtr driver,
                                virDomainObjPtr vm)
 {
+    virErrorPtr err = NULL;
+    int ret = 0;
     size_t i;
 
     for (i = 0; i < vm->def->ndisks; i++) {
@@ -1871,13 +1873,20 @@ qemuMigrationCancelDriveMirror(virQEMUDriverPtr driver,
         if (!diskPriv->migrating || !diskPriv->blockJobSync)
             continue;
 
-        if (qemuMigrationCancelOneDriveMirror(driver, vm, disk) < 0)
-            return -1;
+        if (qemuMigrationCancelOneDriveMirror(driver, vm, disk) < 0) {
+            ret = -1;
+            if (!err)
+                err = virSaveLastError();
+        }
 
         diskPriv->migrating = false;
     }
 
-    return 0;
+    if (err) {
+        virSetError(err);
+        virFreeError(err);
+    }
+    return ret;
 }