Disabling the switch log files not possible

[fschleiss]

If the logging function of P4 switches is disabled in the configuration file, starting the P4 application is not possible.

Reproduce

• In configuration file p4app.json, set "enable_log": true,.
• Try to start p4run.py

Error Output

*** Adding switches:
Traceback (most recent call last):
  File "./../p4-utils/p4utils/p4run.py", line 494, in <module>
    app.run_app()
  File "./../p4-utils/p4utils/p4run.py", line 231, in run_app
    self.create_network()
  File "./../p4-utils/p4utils/p4run.py", line 277, in create_network
    controller=None)
  File "/home/user/p4/data_plane_driven_network_convergence/code/p4-utils/p4utils/mininetlib/p4net.py", line 9, in __init__
    super(P4Mininet, self).__init__(*args, **kwargs)
  File "build/bdist.linux-x86_64/egg/mininet/net.py", line 174, in __init__
  File "/home/user/p4/data_plane_driven_network_convergence/code/p4-utils/p4utils/mininetlib/p4net.py", line 13, in build
    super(P4Mininet, self).build()
  File "build/bdist.linux-x86_64/egg/mininet/net.py", line 502, in build
  File "build/bdist.linux-x86_64/egg/mininet/net.py", line 483, in buildFromTopo
  File "build/bdist.linux-x86_64/egg/mininet/net.py", line 260, in addSwitch
  File "./../p4-utils/p4utils/p4run.py", line 69, in __init__
    P4Switch.__init__(self, *opts, **kwargs)
  File "/home/user/p4/data_plane_driven_network_convergence/code/p4-utils/p4utils/mininetlib/p4_mininet.py", line 92, in __init__
    self.output = open(self.log_file, 'w')
IOError: [Errno 2] No such file or directory: u'/home/user/p4/data_plane_driven_network_convergence/code/p4/log/s1.log'