`-v` option causes frontend to crash if a syslog handler is used

[vkarak]

Config entry for syslog (Mac):

            {
                'type': 'syslog',
                'level': 'INFO',
                'format': '%(message)s',
                'address': '/var/run/syslog'
            }

Normal output:

Command line: ./bin/reframe -C config/tresa.py -c unittests/resources/checks/hellocheck.py -l
Reframe version: 2.18-dev1
Launched by user: karakasv
Launched on host: tresa.local
Reframe paths
=============
    Check prefix      :
    Check search path : 'unittests/resources/checks/hellocheck.py'
    Stage dir prefix     : /Users/karakasv/Repositories/reframe/stage/
    Output dir prefix    : /Users/karakasv/Repositories/reframe/output/
    Perf. logging prefix : /Users/karakasv/Repositories/reframe/perflogs
List of matched checks
======================
  * hellocheck (found in /Users/karakasv/Repositories/reframe/unittests/resources/checks/hellocheck.py)
Found 1 check(s).

Crash:

$ ./bin/reframe -C config/tresa.py -c unittests/resources/checks/hellocheck.py -l -v
Traceback (most recent call last):
  File "./bin/reframe", line 5, in <module>
    cli.main()
  File "/Users/karakasv/Repositories/reframe/reframe/frontend/cli.py", line 263, in main
    printer.inc_verbosity(options.verbose)
  File "/Users/karakasv/Repositories/reframe/reframe/core/logging.py", line 480, in inc_verbosity
    for h in self.std_stream_handlers:
  File "/Users/karakasv/Repositories/reframe/reframe/core/logging.py", line 402, in std_stream_handlers
    return [h for h in self.logger.handlers
  File "/Users/karakasv/Repositories/reframe/reframe/core/logging.py", line 403, in <listcomp>
    if h.stream == sys.stdout or h.stream == sys.stderr]
AttributeError: 'SysLogHandler' object has no attribute 'stream'