IMPALA-3684, IMPALA-3693: Disable core files for breakpad tests
IMPALA-3684, IMPALA-3693: Disable core files for breakpad tests

The breakpad tests were writing core files when triggering minidump
writes. This was actually not needed and interfered with test execution
and artifact collection. Most notably processes would take a long time
to terminate while writing core files (IMPALA-3684). The core files
would also be wrongly collected by Jenkins (IMPALA-3693).

This change adds code to stop test clusters reliably, making
test_breakpad independent from calling setup-impala-cluster.py via
os.system. It also disables core dumps for the duration of the test and
re-enables them afterwards.

Change-Id: If592339632aa662b59be09d911229566d5772321
Reviewed-on: http://gerrit.cloudera.org:8080/3339
Reviewed-by: Michael Brown <97e4d5d0e400e5ad37382425ea95bde8b3933403@cloudera.com>
Reviewed-by: Silvius Rus <f7ea5851fd59d0434c2e152e6169f61c38e0d175@cloudera.com>
Tested-by: Lars Volker <4d73c29a4561048ce85fa0051bb7a6d201781159@cloudera.com>

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