IMPALA-7783: Skip test_default_timezone when testing a real cluster.
IMPALA-7783: Skip test_default_timezone when testing a real cluster.

test_shell_commandline.py::test_default_timezone assumes that the
cluster is running on the same platform as the test process, but
that's only guaranteed when the testing a local minicluster. When
run against a real cluster, the test executor can be a completely
different OS.

Change-Id: Ia4d4c503d2c77136cedd8f3fd830b6ce70d4457f
Reviewed-on: http://gerrit.cloudera.org:8080/11820
Reviewed-by: Impala Public Jenkins <039b6b20426ff68ebe492b3021890d8c8fd010c9@cloudera.com>
Tested-by: Impala Public Jenkins <039b6b20426ff68ebe492b3021890d8c8fd010c9@cloudera.com>

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