syslogd/tests: Address races

I occasionally see failures in the syslogd test suite.  The problem is
that the tests are racy: they send a message using logger(1), then
immediately check whether the message was logged to a log file.  If the
syslogd instance under test doesn't get a chance to run before the
second step, the test fails.

This change reworks things to avoid the race while minimizing the amount
of time sleeping.
1) Each test uses a single logfile, so have them use a new common
   variable, SYSLOGD_LOGFILE, instead of something test-specific.
2) In syslogd_start(), if the configuration references SYSLOGD_LOGFILE,
   wait for it to be created by syslogd before returning.
3) Add a helper syslogd_check_log(), to check for a given log entry in
   the last line of SYSLOGD_LOGFILE, instead of using atf_check
   directly.
4) In syslogd_check_log(), poll the logfile until the desired log entry
   appears, or the test times out.

With this change, I was able to run the tests 1000 times in a loop with
4-way parallelism without seeing any test failures.  Without the change
I usually get a failure within 10 loops.

Reviewed by:	jlduran
MFC after:	2 weeks
Differential Revision:	https://reviews.freebsd.org/D54779

0 files changed, 0 insertions, 0 deletions