Prepare housekeeping interval to be dynamic.

Change housekeeping to be from a fixed interval to a possibly varied
interval decided by nextHousekeeping().
Remove memory storage driver and make empty the default.

This fixes the current cAdvisor HEAD.
Merge pull request #221 from vmarmol/fix

Remove memory storage driver and make empty the default.
Merge pull request #222 from vmarmol/variable-housekeeping

Prepare housekeeping interval to be dynamic.
Updating libcontainer version.

This includes a fix which reduces CPU usage by ~30%.
Merge pull request #228 from vmarmol/update-libcontainer

Updating libcontainer version.