Returns an instance of a bootstrap with the given name.

        This is the only way you should access a bootstrap class, as
        it sets the bootstrap directory correctly.

def get_bootstrap(cls, name, ctx):
        '''Returns an instance of a bootstrap with the given name.

        This is the only way you should access a bootstrap class, as
        it sets the bootstrap directory correctly.
        '''
        if name is None:
            return None
        if not hasattr(cls, 'bootstraps'):
            cls.bootstraps = {}
        if name in cls.bootstraps:
            return cls.bootstraps[name]
        mod = importlib.import_module('pythonforandroid.bootstraps.{}'
                                      .format(name))
        if len(logger.handlers) > 1:
            logger.removeHandler(logger.handlers[1])
        bootstrap = mod.bootstrap
        bootstrap.bootstrap_dir = join(ctx.root_dir, 'bootstraps', name)
        bootstrap.ctx = ctx
        return bootstrap