IMPALA-8114: Deflake test_breakpad.py
IMPALA-8114: Deflake test_breakpad.py

A test failed recently in a private build and it looked like the loop in
wait_for_num_processes had terminated to early. To make sure that the
forked of processes that write the minidumps have actually started, we
now sleep for 1 second before entering the wait loop.

Change-Id: Ifcd1fbb498c475a1f186f490abaf90b47ecba05b
Reviewed-on: http://gerrit.cloudera.org:8080/12273
Reviewed-by: Tim Armstrong <2f8e34250f03a653da3dc27f7ec203eafdde80fc@cloudera.com>
Tested-by: Impala Public Jenkins <039b6b20426ff68ebe492b3021890d8c8fd010c9@cloudera.com>

cloudera/Impala,cloudera/Impala,cloudera/Impala,cloudera/Impala,cloudera/Impala,cloudera/Impala,cloudera/Impala