IMPALA-4920: custom cluster tests: fix generation of py.test options
IMPALA-4920: custom cluster tests: fix generation of py.test options

This patch fixes a problem in which unnecessary quote characters were
part of some impala-py.test arguments for running the custom cluster
tests. The bug was causing py.test metadata files as described by the
py.test options --junit-xml and --result-log to end up outside the
intended path for such artifacts. By removing the unnecessary escaped
quotes, custom cluster py.test metadata artifacts will now be in the
proper location. I doubly made sure it was safe to remove these quotes
by adding a space in the RESULTS_DIR. The space isn't expanded but is
instead properly treated as part of RESULTS_DIR.

Change-Id: If6a56bc6bca826a8b50340e5caea7687441899e6
Reviewed-on: http://gerrit.cloudera.org:8080/5978
Reviewed-by: Jim Apple <396f577ccd0f19e47f0fb44dae1d6fc43cc20400@apache.org>
Tested-by: Impala Public Jenkins

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