Fix the bug mentioned in [TACHYON-66]

Fix the bug mentioned in [TACHYON-66] "The memory usage statistics is
not right when multi-user cache the same file and stops their
connection".
Change the synchronized range
Add a unit test for cacheBlock

Add a unit test for cacheBlock
stop can target a component
Merge remote-tracking branch 'upstream/master' into TACHYON-66
Update the UT to be concurrent

Update the UT to be concurrent and merge with the latest master branch.
Update the test code

Update the test code
Merge pull request #354 from PasaLab/TACHYON-66

[TACHYON-66] Fix the bug of the memory usage statistics in tachyon.worker.WorkerStorage
Merge pull request #375 from dcapwell/kill-component

stop can target a component
[TACHYON-62] Implement a Netty based DataServer
upgraded netty.  moved worker shutdown after boss.  style
got transferTo to pass tests
refactor pipeline and added commented out code for next test
enable switch between epoll and nio
testing out epol with file region
moved file region logic to response encoder
moved nio server to nio package.  made a new DataServer interface to abstract over the implementations
pluggable network type
added sync group
more opts for netty