test/exclude line starting with MemAvailable

tested for line starting w/ 'MemAvailable' and exclude from used memory
calculation by simply decrementing the index variable by 1 and
proceeding

this is not the most robust way to deal with this as it still assumes that the correct entries are in the first 5 lines of /proc/meminfo, but this is a quick fix that has been tested on both the old (3.13.10-200) and new (3.14.2-200) kernels of Fedora 20

Closes #8