Removed 'message' keyword when raising Error

The exception handler for listing nova images (now glance images)
was raising an unexpected argument exception because Error() was
getting called with a 'message' keyword. Removed the keyword in
line with elsewhere.

Change-Id: If928aec0bb807495a00b8447a69c4e3dea43fb3b
Closes-Bug: 1315456
Merge "Removed 'message' keyword when raising Error"