Several refactoring steps about common lab elements and logger
 - LaboratoryElement is a parent class for all machines and switches, checking name
 - reunite logger methods and classes in logger.py
 - add LoggerMixin to automatically inject logger in class
 - adding test_logger.py to test LoggerMixin
 - convert all project classes to use LoggerMixin
Adding _start() and _shutdown() abstract methods in LaboratoryElement (enforced with abc)
Add doctring to class LaboratoryElement
Add test for testbed01 with sequential mode
removing unnecessary method name in error message from readable_dir
sequential mode in False by default in the Lab
missing return carrier in lhalt
removing useless lines
Merge branch 'develop' into feature/refactoring-v0.0.1
moving element.py and logger.py to new src directory
moving test_logger.py to new src directory
Merge branch 'develop' into feature/refactoring-v0.0.1
updating gitignore
forcing buildout v2.1.1
zc.buildout version not fixed in buildout.cfg
removing reference to distribute in setup.py
fixes #4 : generated random number is independant of the architecture
use find_packages() to discover packages in setup.py
Removing DEFAULT_MACHINE_* and DEFAULT_NETKYTHON_DIR from __init__

- still some tests are failling
Fixing lstart import