[SPARK-2953] Allow using short names for io compression codecs

Instead of requiring "org.apache.spark.io.LZ4CompressionCodec", it is easier for users if Spark just accepts "lz4", "lzf", "snappy".

Author: Reynold Xin <rxin@apache.org>

Closes #1873 from rxin/compressionCodecShortForm and squashes the following commits:

9f50962 [Reynold Xin] Specify short-form compression codec names first.
63f78ee [Reynold Xin] Updated configuration documentation.
47b3848 [Reynold Xin] [SPARK-2953] Allow using short names for io compression codecs

(cherry picked from commit 676f98289dad61c091bb45bd35a2b9613b22d64a)
Signed-off-by: Reynold Xin <rxin@apache.org>