finished the unit test of the filename input plugin

@klaus This test is written using the Embulk test tool in the Embulk-tests thus the input plugin is the testing plugin(filename) but the parser is defaultly using the csv(I try to use the thrid party plugin like the none or none-bin but it fails). Therefore, I use a simple csv(in the resources/data/test.csv) file as the testing file. Test if it contain the filename in its output File.