correct get_modules_tools function, rename 'check_usable' to 'check_useable', fix modules unit tests by initializing config
get rid of modules_tool global var
use get_modules_tool instead of config.modules_tool global var, rename self.modules to self.modules_tool, pass modules_tool to EasyConfig
add modules_tool constructor argument, pass it through to toolchain constructor
add modules_tool constructor argument and use it, rename self.modules to self.modules_tool
use config.get_modules_tool instead of config.modules_tool global var
fix log warning for unavailable module tools
fix unit tests w.r.t. changes in modules.py