default celeryconfig.cfg points to wrong DHCP_LEASES_FILE location

[Diogo Matsubara]

Tested on maas - 0.1+bzr1063+dfsg-0+1093+98~ppa0~quantal1
Once you install the package the default /etc/maas/celeryconfig.py points to DHCP_LEASES_FILE = '/var/lib/maas/dhcpd.leases'
 when it should be DHCP_LEASES_FILE = '/var/lib/maas/dhcp/dhcpd.leases'

This causes the following error running the upload_dhcp_leases task:

[2012-09-27 20:31:57,015: ERROR/MainProcess] Task provisioningserver.tasks.upload_dhcp_leases[0a44ce9b-51a2-4af9-88b2-71c65441b7ab] raised exception: IOError(2, 'No such file or directory')
Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/celery/execute/trace.py", line 181, in trace_task
    R = retval = fun(*args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/provisioningserver/tasks.py", line 261, in upload_dhcp_leases
    upload_leases()
  File "/usr/lib/python2.7/dist-packages/provisioningserver/dhcp/leases.py", line 153, in upload_leases
    timestamp, leases = parse_leases_file()
  File "/usr/lib/python2.7/dist-packages/provisioningserver/dhcp/leases.py", line 76, in parse_leases_file
    with open(DHCP_LEASES_FILE, 'rb') as leases_file:
IOError: [Errno 2] No such file or directory