Misc stress test updates
Misc stress test updates

Changes:
1) IMPALA-3121: Don't ignore backend <-> backend timeout errors.
2) Only collect query profiles if they are really needed. A v-tune
   profile showed 10% cpu time collecting query profiles. Previously the
   stress test would unconditionally collect a query profile even if the
   profile wouldn't be used.
3) Add CLI options to control runtime info reliability. The work was
   already done but there were no CLI params (they had to be hard
   coded). Now --samples and --max-conflicting-samples are available.

Change-Id: Ia7bd39861162e85b9091a0ef41ed1c317737e66c
Reviewed-on: http://gerrit.cloudera.org:8080/2504
Reviewed-by: Casey Ching <77bc9a9984e6786c5799d7a71768cf023120ef76@cloudera.com>
Tested-by: Casey Ching <77bc9a9984e6786c5799d7a71768cf023120ef76@cloudera.com>

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