(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 it would be good to have the message express the memory needed in terms of the current heap size (e.g., `* 1.1 heap-size`) rather than hard-coding 2 GB.