Proposed update to Linux partition_test

[dragosprisaca]

The documentation for statfs function (http://linux.die.net/man/2/statfs) defines the following two properties: fsblkcnt_t f_bfree (free blocks in fs) and fsblkcnt_t f_bavail (free blocks available to unprivileged users), but only the first one is specified in the OVAL partition_state and partition_item (please see the space_left entity).
I am proposing to add a new entity (i.e. space_left_for_unprivileged_users) to record the free blocks available to unprivileged users.

Related issue: #262

Respectfully,
_Dragos.