pci-assign: Clean up "Failed to assign" error messages

The arguments of error_setg() & friends should yield a short error
string without newlines.

Two places try to append additional help to the error message by
embedding newlines in the error string.  That's nice, but let's do it
the right way, with error_append_hint().

Cc: Laszlo Ersek <lersek@redhat.com>
Signed-off-by: NMarkus Armbruster <armbru@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
Message-Id: <1450452927-8346-20-git-send-email-armbru@redhat.com>
Reviewed-by: NLaszlo Ersek <lersek@redhat.com>

hw/i386/kvm/pci-assign.c

@@ -770,7 +770,7 @@ static char *assign_failed_examine(const AssignedDevice *dev)
         "*** $ echo \"%04x:%02x:%02x.%x\" > /sys/bus/pci/drivers/"
         "pci-stub/bind\n"
         "*** $ echo \"%04x %04x\" > /sys/bus/pci/drivers/pci-stub/remove_id\n"
-        "***",
+        "***\n",
         ns, dev->host.domain, dev->host.bus, dev->host.slot,
         dev->host.function, vendor_id, device_id,
         dev->host.domain, dev->host.bus, dev->host.slot, dev->host.function,
@@ -778,7 +778,7 @@ static char *assign_failed_examine(const AssignedDevice *dev)
         dev->host.function, vendor_id, device_id);
 
 fail:
-    return g_strdup("Couldn't find out why.");
+    return g_strdup("Couldn't find out why.\n");
 }
 
 static void assign_device(AssignedDevice *dev, Error **errp)
@@ -812,8 +812,9 @@ static void assign_device(AssignedDevice *dev, Error **errp)
             char *cause;
 
             cause = assign_failed_examine(dev);
-            error_setg_errno(errp, -r, "Failed to assign device \"%s\"\n%s",
-                             dev->dev.qdev.id, cause);
+            error_setg_errno(errp, -r, "Failed to assign device \"%s\"",
+                             dev->dev.qdev.id);
+            error_append_hint(errp, "%s", cause);
             g_free(cause);
             break;
         }
@@ -912,11 +913,10 @@ retry:
             dev->features |= ASSIGNED_DEVICE_PREFER_MSI_MASK;
             goto retry;
         }
-        error_setg_errno(errp, -r,
-                         "Failed to assign irq for \"%s\"\n"
-                         "Perhaps you are assigning a device "
-                         "that shares an IRQ with another device?",
+        error_setg_errno(errp, -r, "Failed to assign irq for \"%s\"",
                          dev->dev.qdev.id);
+        error_append_hint(errp, "Perhaps you are assigning a device "
+                          "that shares an IRQ with another device?\n");
         return r;
     }