This commit is to change feature files to made them  more understanbale. Details are below.

***Separate "flow_manager.feature" file into 3 files below and add some description.
deleted:    features/flow_manager.feature
new file:   features/flow_manager_hop.feature
new file:   features/flow_manager_module.feature
new file:   features/flow_manager_path.feature

***Fiexed to suppress the error of trema's command test.
modified:   features/support/hooks.rb

***Add new tests.
new file:   src/flow_manager/flow_manager_test/flow_manager_hop_test.rb
new file:   src/flow_manager/flow_manager_test/flow_manager_multiple_path_teardown_by_manual_test.rb
new file:   src/flow_manager/flow_manager_test/flow_manager_path_test.rb

***Modified test files below to make them more understandable codes.
modified:   src/flow_manager/flow_manager_test/flow_manager_module_setup_test.rb
modified:   src/flow_manager/flow_manager_test/flow_manager_module_teardown_by_match_test.rb
modified:   src/flow_manager/flow_manager_test/flow_manager_module_teardown_test.rb
modified:   src/flow_manager/flow_manager_test/flow_manager_multiple_path_setup_test.rb
modified:   src/flow_manager/flow_manager_test/flow_manager_path_setup_duplicate_test.rb
modified:   src/flow_manager/flow_manager_test/flow_manager_path_setup_test.rb
modified:   src/flow_manager/flow_manager_test/flow_manager_path_teardown_by_manual_test.rb
modified:   src/flow_manager/flow_manager_test/flow_manager_module_lookup_test.rb

***Deleted the unused file.
deleted:    src/flow_manager/flow_manager_test/flow_manager_path_setup_with_negative_hop_.rb