Update 'drive_stats.pl' to report last drives media has been loaded into

Add to report the last 4 drives this media has been loaded into.
e.g.
Media previously mounted in  : [IBM     XYZZY_A2  ]
Media previously mounted in  : [HP      XYZZY_A1  ]
Media previously mounted in  : []
Media previously mounted in  : []

Signed-off-by: Mark Harvey <markh794@gmail.com>