Minor code cleanup
merge HostWithPrivateDirs into Host
use a single mininet instance in bindpy
added documentation for HostWithPrivateDirs
mountprivatedirs is no longer needed
added persistence option to HostWithPrivateDirs. also attached mount namespaces when mnexec -a is specified
Added support for mount namespaces in bind.py. Also moved it to the node class as a host type.
Pass code check (except bogus Popen error)
Change API for more efficient remount and unmount.
Prototype implementation of bind mounts.