IMPALA-6232: Disable file handle cache by default
IMPALA-6232: Disable file handle cache by default

There are scenarios where HDFS file appends or HDFS file
overwrites can lead to HDFS disabling short circuit reads.
Since this can be a performance regression, this changes
the default value for max_cached_file_handles to 0 to
disable the file handle cache by default. This also changes
the default value for unused_file_handle_timeout_sec to 270.
If users enable the file handle cache, this setting will
prevent some of the scenarios that disable short circuit
reads.

Ran existing file handle cache tests to verify that there
is no impact.

Change-Id: Iea7f943f63b72b42286a9e8b9987308baa79d7b0
Reviewed-on: http://gerrit.cloudera.org:8080/8750
Reviewed-by: Joe McDonnell <2f04924382c6a21f96a9a4f8cbedc35ff4599584@cloudera.com>
Tested-by: Impala Public Jenkins

cloudera/Impala,cloudera/Impala,cloudera/Impala,cloudera/Impala,cloudera/Impala,cloudera/Impala,cloudera/Impala