WiredTiger default configuration should be adjusted for laptop (e.g. default cache size should be <2G)

On laptops (mac or windows client) , when users evaluate with WT

1) The current default of ½ RAM size likely to be too greedy and will cause a significant competition on RAM w/ other apps (which leads to high amount of page faults)
2) The situation will be amplified if users will evaluate a replica set as our mongod apps will compete on memory
3) The laptop processor HW is usually lower then server (no L3 cache and etc)
4) Higher cache size longer I/O pressure during checkpoint
5) My initial verification on an empty Mac (OSX) produce the following results

YCSB 50/50 load phase (insert only) measured on 3.1.4-pre-

It’s easy to detect the Mac OS or windows client platforms and adjust our default for this platform