exposes the YARN client ContainerRequest hosts and racks options into ResourceSpecification #TWILL-40

Signed-off-by: Terence Yim <terence@continuuity.com>
fixing checkstyle violations #TWILL-40

Signed-off-by: Terence Yim <terence@continuuity.com>
made changes as per review #18209 for #TWILL-40

Signed-off-by: Terence Yim <terence@continuuity.com>
made changes as per review #18209 for #TWILL-40 rev2

Signed-off-by: Terence Yim <terence@continuuity.com>