GPII-920: Modify USB lib grunt tasks to handle non-fatal errors gracefully.

Added -p flag to mkdir command so as to not fail if the directory
already exists (installUsbLib).

Added -r flag to rm of /var/lib/gpii directory to handle non-empty
directory (uninstallUsbLib).
Merge remote-tracking branch 'klown/master'

* klown/master:
  GPII-920: Modify USB lib grunt tasks to handle non-fatal errors gracefully.