updated: fix apt-get clean failure

 E: Could not get lock /var/cache/apt/archives/lock
  - open (11: Resource temporarily unavailable)

This is because the python-apt bindings don't close their file descriptors
on object deletion.

So we move the code to a position the process handling with the apt-cache
has terminated and so all apt fd's are closed

Signed-off-by: Manuel Traut <manut@linutronix.de>