(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.
Not a big deal but our other functions that validate something and throw an exception follow a pattern like `validate-foo!`.  Maybe `validate-memory-requirements!` or something? Just nitpicking at this point...