Added file check before reading config files, Fixes #666

[DarKnight24]

The config files will be checked for existence before reading it, to prevent exception.

Related Issue

issue #666

Motivation and Context

Reviewers

@delta24 @DePierre

How Has This Been Tested?

Delete the config file in profile folder and try to run OWTF

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Other

Checklist:

• My code follows the code style (modified PEP8) of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.

[DePierre]

Would it be better to, instead of relying on db error handler, get the component directly?

For instance something like:

class ConfigDB(BaseComponent, DBConfigInterface):

    COMPONENT_NAME = "db_config"

    def __init__(self):
         # . . .
        self.error_handler = self.get_component("error_handler")
    # . . .
    def LoadConfigDBFromFile(self, file_path):
        # . . .
        if not os.path.isfile(file_path):  # Check if the config file exists.
            self.error_handler.FrameworkAbort("Config file not found at: %s" % file_path)

Also could you make sure you follow pep8? With the missing surrounding spaces and the proper inline comment format.

[DePierre]

@DarKnight-- Thank you very much! :)