[SPARK-11236][CORE] Update Tachyon dependency from 0.7.1 -> 0.8.0.

Upgrades the tachyon-client version to the latest release.

No new dependencies are added and no spark facing APIs are changed. The removal of the `tachyon-underfs-s3` exclusion will enable users to use S3 out of the box and there are no longer any additional external dependencies added by the module.

Author: Calvin Jia <jia.calvin@gmail.com>

Closes #9204 from calvinjia/spark-11236.