Add storage dir and eviction strategy [TACHYON-33][SubTask 2 & 3]

resubmitted for PR361, rebase to current master.
Can you move the lock docs at the references themselves? We don't use jsr-305, but thats how `GuardedBy` works, and I tend to find the code is easier to read when the docs for what locks are needed are at the variable.

https://jsr-305.googlecode.com/svn/trunk/javadoc/javax/annotation/concurrent/GuardedBy.html