Improve fix wrong code generation if EN/ENO are used in FBD/LD/SFC

Commit c9915bc6 "Fix wrong code generation if EN/ENO are used in
FBD/LD/SFC" caused following backtrace in some cases:

File "/home/developer/WorkData/PLC/beremiz/beremiz/PLCGenerator.py", line 476, in GenerateProgram
self.GeneratePouProgram(pou_name)
File "/home/developer/WorkData/PLC/beremiz/beremiz/PLCGenerator.py", line 258, in GeneratePouProgram
program = pou_program.GenerateProgram(pou)
File "/home/developer/WorkData/PLC/beremiz/beremiz/PLCGenerator.py", line 1713, in GenerateProgram
self.ComputeProgram(pou)
File "/home/developer/WorkData/PLC/beremiz/beremiz/PLCGenerator.py", line 997, in ComputeProgram
eno_var = self.GetUsedEno(body, connections)
File "/home/developer/WorkData/PLC/beremiz/beremiz/PLCGenerator.py", line 929, in GetUsedEno
for invar in blk.inputVariables.getvariable():
File "/home/developer/WorkData/PLC/beremiz/beremiz/xmlclass/xmlclass.py", line 1363, in getattrMethod
return DefaultElementClass.__getattribute__(self, name)
<type 'exceptions.AttributeError'>: 'inOutVariable' object has no attribute 'inputVariables'

Crossbar test router configuration is available in .crossbar directory.

Starting command:
crossbar start

This project contains wamp client config to be loaded at runtime startup.

project_files/wampconf.json

wampconf.json is in "Project Files", so it is copied to runtime's working directory, and then loaded after program transfer + runtime restart.

Otherwise, wamp config file path can be forced :
./Beremiz_service.py -c /path/to/my/wampconf.json /working/dir

Otherwise, path for CRA secret can be forced :
./Beremiz_service.py -s /path/to/my/secret /working/dir

Tested on version:
 Crossbar.io        : 17.12.1 (Crossbar.io COMMUNITY)
   Autobahn         : 17.10.1 (with JSON, MessagePack, CBOR, UBJSON)
   Twisted          : 17.9.0-EPollReactor
   LMDB             : 0.93/lmdb-0.9.18
   Python           : 2.7.12/CPython