write ch plus various fixes.
Merge branch 'master' of github.com:amplab/tachyon
mkdir returns true/false
use master hostname in conf/tachyon-env.sh as default.
show disk usage
user NoWorkerException instead of NoLocalWorkerException
fix null pointer bug in blockinstream
add replication and blocksize parameter to underfs interface.
temp fix for replication factor for hdfs
fix of bin/start.sh hangs by redirecting output to the null device.
Merge pull request #36 from hobinyoon/master

fix of bin/start.sh hangs by redirecting output to the null device.
fix of the bin/format.sh error.
Merge pull request #38 from hobinyoon/master

fix of the bin/format.sh error.
better underfs util.
specify mount size for linux ramfs.
s3n support
conform to the coding style
Merge pull request #40 from hobinyoon/master

s3n support