(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 think this would be clearer as `(/ heap-size 0.9)`.

Also, why 90%?  Seems reasonable, but I'm curious where that number came from.