[SPARK-14342][CORE][DOCS][TESTS] Remove straggler references to Tachyon

## What changes were proposed in this pull request?

Straggler references to Tachyon were removed:
- for docs, `tachyon` has been generalized as `off-heap memory`;
- for Mesos test suits, the key-value `tachyon:true`/`tachyon:false` has been changed to `os:centos`/`os:ubuntu`, since `os` is an example constrain used by the [Mesos official docs](http://mesos.apache.org/documentation/attributes-resources/).

## How was this patch tested?

Existing test suites.

Author: Liwei Lin <lwlin7@gmail.com>

Closes #12129 from lw-lin/tachyon-cleanup.

1 files changed, 1 insertions, 1 deletions

diff --git a/docs/streaming-programming-guide.md b/docs/streaming-programming-guide.md
index 8d21917a7d..7f6c0ed699 100644
--- a/docs/streaming-programming-guide.md
+++ b/docs/streaming-programming-guide.md
@@ -2178,7 +2178,7 @@ overall processing throughput of the system, its use is still recommended to ach
 consistent batch processing times. Make sure you set the CMS GC on both the driver (using `--driver-java-options` in `spark-submit`) and the executors (using [Spark configuration](configuration.html#runtime-environment) `spark.executor.extraJavaOptions`).
 
 * **Other tips**: To further reduce GC overheads, here are some more tips to try.
-    - Use Tachyon for off-heap storage of persisted RDDs. See more detail in the [Spark Programming Guide](programming-guide.html#rdd-persistence).
+    - Persist RDDs using the `OFF_HEAP` storage level. See more detail in the [Spark Programming Guide](programming-guide.html#rdd-persistence).
     - Use more executors with smaller heap sizes. This will reduce the GC pressure within each JVM heap.