TACHYON-182 Add checkstyle to the maven build system so we could reduce time to do style check for contributions

TACHYON-182 Add checkstyle to the maven build system so we could reduce time to do style check for contributions following Google style.
Fixed violations reported in the current master branch.

Note that currently you need to run
  mvn checkstyle:check or mvn checkstyle:checkstyle
to run the check.

You will see some warnings on public member for Tachyon configuration classes:
  CommonConf
  MasterConf
  WorkerConf
  UserConf
due to naming of their public member as all caps.

Once we stabilize the code we could hook it to build system to fail when checkstyle fail.
All member variables need to follow pattern of prefix with m. Do we want to
make exception for public variables ?
I would reccommed keep it consistent to have all non static member
variables to be prefixed with m and the camel case.

On Saturday, October 18, 2014, Haoyuan Li <notifications@github.com> wrote:

> In core/src/main/java/tachyon/client/TachyonByteBuffer.java:
>
> > @@ -9,7 +9,7 @@
> >   */
> >  public class TachyonByteBuffer implements Closeable {
> >    // ByteBuffer contains data.
> > -  public final ByteBuffer DATA;
> > +  public final ByteBuffer mData;
> >
> >    private final long mBlockId;
>
> Should be BLOCK_ID?
>
> —
> Reply to this email directly or view it on GitHub
> <https://github.com/amplab/tachyon/pull/473/files#r19057749>.
>