Create free_ssd_space_check.pl

# We had a small crisis when our SSD pool filled up and caused
# some problems on our prod cluster.  Since this data isn't exposed
# in isilon SNMP implementation, we worked with their Support team
# which helped us find the right way to show this space.
#
# isiprod01-1# perl /ifs/data/scripts/free_ssd_space_check.pl
# free_ssd_blocks :: 696097467 total_ssd_blocks :: 866908404 :: percent_used :: 19.70
# isiprod01-1#
#
# Some graphing tools perfer raw numbers.  Just uncomment the free or total
# if your stats db wants to do the math on its own, or track the two values
# in different places.