(SERVER-4) Add memory check to Master Service

Add a memory check to the Master service's init function that,
when the /proc/meminfo file exists, parses it to get the total
amount of RAM on the system and fails if the total JVM heap
size is greater than 90% of RAM.
I know this isn't entirely helpful rightnow, but we could pretty easily get numbers on the base amount of ram, then the ram needed for each pooled JRuby interpreter. 

:see_no_evil: