Avoid cyclic imports

[Marco Giusti]

How to reproduce the problem:

 $ python -c "from virtualbricks import virtualmachines"

 Traceback (most recent call last):
   File "<string>", line 1, in <module>
   File "/usr/local/lib/python2.7/dist-packages/virtualbricks/virtualmachines.py", line 30, in <module>
  from virtualbricks.bricks import Brick
   File "/usr/local/lib/python2.7/dist-packages/virtualbricks/bricks.py", line 32, in <module>
  from virtualbricks.gui.graphics import Icon, Topology
   File "/usr/local/lib/python2.7/dist-packages/virtualbricks/gui/__init__.py", line 1, in <module>
  from .gui import VBGUI
   File "/usr/local/lib/python2.7/dist-packages/virtualbricks/gui/gui.py", line 34, in <module>
  from virtualbricks.brickfactory import BrickFactory
   File "/usr/local/lib/python2.7/dist-packages/virtualbricks/brickfactory.py", line 40, in <module>
  from virtualbricks.bricks import Brick
 ImportError: cannot import name Brick

This happens when lower modules depends on higer modules and vice versa.
A temporary solution is to import `virtualbricks.gui.gui` (maybe
`virtualbricks.gui.graphics`?) before all the others module but this
patch stinks.

 affects virtualbrick

[Marco Giusti (marco-giusti)]

This is fixed but the commit was lost in time.