Global name 'isodir' is not defined

In function VMBuilder::plugins::ubuntu::dapper::Dapper::debootstrap_mirror variable isodir isn't set.

I fixed it by setting it in the consructor of the suite class (see attached patch)

Traceback (most recent call last):
  File "./vmbuilder", line 29, in <module>
    VMBuilder.run()
  File "/home/ar/vcs/lp/vmbuilder/VMBuilder/__init__.py", line 66, in run
    frontend.run()
  File "/home/ar/vcs/lp/vmbuilder/VMBuilder/plugins/cli/__init__.py", line 67, in run
    vm.create()
  File "/home/ar/vcs/lp/vmbuilder/VMBuilder/vm.py", line 456, in create
    self.install()
  File "/home/ar/vcs/lp/vmbuilder/VMBuilder/vm.py", line 395, in install
    self.distro.install(self.installdir)
  File "/home/ar/vcs/lp/vmbuilder/VMBuilder/plugins/ubuntu/distro.py", line 131, in install
    self.suite.install(destdir)
  File "/home/ar/vcs/lp/vmbuilder/VMBuilder/plugins/ubuntu/dapper.py", line 50, in install
    self.debootstrap()
  File "/home/ar/vcs/lp/vmbuilder/VMBuilder/plugins/ubuntu/dapper.py", line 206, in debootstrap
    cmd = ['/usr/sbin/debootstrap', '--arch=%s' % self.vm.arch, self.vm.suite, self.destdir, self.debootstrap_mirror()]
  File "/home/ar/vcs/lp/vmbuilder/VMBuilder/plugins/ubuntu/dapper.py", line 211, in debootstrap_mirror
    os.mkdir(isodir)
NameError: global name 'isodir' is not defined