Correct PR #30

[duboism]

This PR addresses some errors introduced by #30. There are 2 classes of errors.

First, direct downloaders were broken and I missed that:

• In some cases (particularly for POST resources) the remote server may not support HEAD and return 405 which makes DirectHTTPDownload.list() fail while we can simply ignore this error in this case.
• Similarly, the way we use cURL in DirectFTPDownload.list() leads to return code 350 which is OK but causes the method to fail.

Next, tests in PR #30 were flawed and therefore some errors were not detected. The main errors here are:

• assertRegexp no longer exists (it was replaced by assertRegex) but this was not detected because it was in assertRaises context. While at it, we don't use anymore the deprecated assertRaisesRegexp (the history of names in unittest can be found here).
• Use of assertLogs and the regex used in test were incorrect but this was not detected for the same reason.
• Errors in RSYNCDownload.list() were not correctly logged but it was detected.

Last but not least, IRODSDownload was not updated.

Status:

• Errors due to flawed tests and in RSYNCDownload are corrected.
• Regarding DirectHTTPDownload.list(), we explicitly consider 405 as a non-error in this case but we won't get metadata.
• Regarding DirectFTPDownload.list(), we explicitely consider 350 a correct return code in this case.
• IRODSDownload.list() now raises exceptions and log messages as other downloaders.

[osallou]

405 error code is returned in test, but i do not know if this is always the case with all servers. Maybe should be tested with a local python flask app for example to be sure

[osallou]

Comment on my comment, after thinking about previous other tests, if head is not supported, yes 405 will be raised, and we should just continue in this case. In case of other errors, ok to raise exception