Removed warning on MAX_MACHINES = 0.

* With the new VMPool object, MAX_MACHINES = 0 will not do anything
  remotely desirable.
Added new VMPool object.
Added VMPool object to fix #232.
Merge branch 'issue232' into v0.2dev

Conflicts:
	galah/sheep/virtualsuites/vz/vmpool.py
	galah/sheep/virtualsuites/vz/vz.py