IMPALA-4659: fuzz test fixes
IMPALA-4659: fuzz test fixes

* Apply a 512m mem_limit to all fuzz tests. This limits aggregate memory
  consumption to ~5GB per daemon(assuming 10 concurrent tests).
* Refactor the exec option handling to use the exec_option dimension.
  This avoids executing the test multiple times redundantly
* Remove the xfails to reduce noise, since there is no immediate plan to
  fix the product bugs. Instead just pass the tests.

Testing:
Ran in a loop for ~1h to flush out flakiness.

Change-Id: Ie1942ceef252ec3e6171a0a54722b66a7d9abbd7
Reviewed-on: http://gerrit.cloudera.org:8080/5502
Reviewed-by: Tim Armstrong <2f8e34250f03a653da3dc27f7ec203eafdde80fc@cloudera.com>
Tested-by: Impala Public Jenkins

michaelhkw/incubator-impala,michaelhkw/incubator-impala,cloudera/Impala,michaelhkw/incubator-impala,michaelhkw/incubator-impala,michaelhkw/incubator-impala,cloudera/Impala,michaelhkw/incubator-impala,cloudera/Impala,cloudera/Impala,michaelhkw/incubator-impala,cloudera/Impala,cloudera/Impala,cloudera/Impala