Fix for the isDir function in the FTP Adapter

[Romain]

The isDir function seems to be broken in the FTP Adapter.
When I try to retrieve a document through a stream, I get this error: ftp_chdir(): /documents/your-file-name.jpg: No such file or directory

Here is the complete trace:

in vendor/knplabs/gaufrette/src/Gaufrette/StreamWrapper.php->stat (line 210) 
in vendor/knplabs/gaufrette/src/Gaufrette/Stream/InMemoryBuffer.php->isDirectory (line 159) 
in vendor/knplabs/gaufrette/src/Gaufrette/Filesystem.php->isDirectory (line 333)
in vendor/knplabs/gaufrette/src/Gaufrette/Adapter/Ftp.php->isDir (line 222)
in vendor/knplabs/gaufrette/src/Gaufrette/Adapter/Ftp.phpftp_chdir (line 369)
in vendor/knplabs/gaufrette/src/Gaufrette/Adapter/Ftp.php (line 369)

Changing the way we perform this test by using the PHP function is_dir instead of the ftp_chdir one fixes this error.

[Romain]

I created a private method for the connection URL.
I also kept the chdir method as the main approach and fallback on is_dir with passive mode set to true if we catch and exception with chdir.

[nicolasmure]

Thanks for the update ;)

[Romain]

@nicolasmure I pushed a fix with your comments applied in it.

[nicolasmure]

Can you also squash your commits please ? :)

[Romain]

@nicolasmure Got it. Pushed a change accordingly to your comment.

[nicolasmure]

Thanks for the changes :)

There are also some failing tests, do you mind to fix them ?

phpunit :

There were 2 failures:
1) Gaufrette\Functional\Adapter\FtpTest::shouldCheckIfFileExists
Failed asserting that true is false.
/home/travis/build/KnpLabs/Gaufrette/tests/Gaufrette/Functional/Adapter/FunctionalTestCase.php:91

2) Gaufrette\Functional\Adapter\FtpTest::shouldFailWhenTryMtimeForKeyWhichDoesNotExist
Failed asserting that 1561017417 is false.
/home/travis/build/KnpLabs/Gaufrette/tests/Gaufrette/Functional/Adapter/FunctionalTestCase.php:119

and also the phpspec for this adapter.

You can run the specs with

$ docker/run-task php7.2 vendor/bin/phpspec run spec/Gaufrette/Adapter/Ftp.php

and the integration tests with

$ docker/run-task php7.2 vendor/bin/phpunit tests/Gaufrette/Functional/Adapter/FtpTest.php

[Romain]

Your comments have been integrated. These are nice improvements. ;)

[nicolasmure]

Can you also update the tests accordingly please ?

[Romain]

@nicolasmure I'm not sure how to update the tests since they're not checking the way we connect to the server.