REGRESSION usb-creator and Ubuntu USB policies set up impossible situation

[Jeff Lane ]

Because Ubuntu automatically mounts USB sticks, this creates a bit of an impossible situation with erasing a disk via usb-creator.

Steps to reproduce:
1: log in as normal user
2: Plug in the USB stick you want to use as an Ubuntu boot device (Note that Ubuntu will automount it)
2: open terminal
3: run usb-creator-gtk via sudo to work around policy kit stupidity that prevents normal users from formatting usb disks.
4: select your USB device
5: Click Erase Disk
6: Get a popup error that says:
org.freedesktop.DBus.Python.gi._glib.GError: Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/dbus/service.py", line 707, in _message_cb
    retval = candidate_method(self, *args, **keywords)
  File "/usr/share/usb-creator/usb-creator-helper", line 235, in Format
    block.call_format_sync('vfat', GLib.Variant('a{sv}', {'label': GLib.Variant('s', '')}), None)
gi._glib.GError: GDBus.Error:org.freedesktop.UDisks2.Error.Failed: Error creating file system: Command-line `mkfs.vfat -I -n "" "/dev/sdb1"' exited with non-zero exit status 1:
stdout: `mkfs.fat 3.0.26 (2014-03-07)
'
stderr: `mkfs.vfat: /dev/sdb1 contains a mounted filesystem.
'

This is another regression in usb-creator. This problem did NOT exist at all when I used it on Trusty Betas.

In the past, usb-creator seemed good enough to just delete the files, not try to re-format the device itself.

[Liam P. White (liampwhite)]

Confirmed on Ubuntu-GNOME 14.04 release, clean install.