cleanup/sftp: "Couldn't delete file: Failure'" only logged on level 9

[Daniel Hahler]

With verbosity 8 I am getting the following log entries:
sftp command: 'rm "duplicity-full.20101022T002340Z.vol1.difftar.gpg"'
sftp command: 'rm "duplicity-full.20101022T002340Z.vol2.difftar.gpg"'

Only using the max verbosity (9) the error shows up:
sftp command: 'rm "duplicity-full.20101022T002340Z.vol1.difftar.gpg"'
State = sftp, Before = 'rm "duplicity-full.20101022T002340Z.vol1.difftar.gpg"^M
Removing /moby/duplicity-full.20101022T002340Z.vol1.difftar.gpg^M
Couldn't delete file: Failure'

(note that there are extra ^M characters for messages of this level, too).

These errors should show up on every level, but apparently on the default log level of 4.

This is duplicity 0.6.10.

From a quick glance at the source in duplicity/backends/sshbackend.py it looks like there is nothing implemented to log error responses from sftp, and also child.exitstatus does not reflect the failure.

[Daniel Hahler (blueyed)]

I am attaching a branch/patch meant to fix this, but have not tested it.

If you're unsure if this fix works, I can setup a test environment (i.e. fill up the backup space again and hope that it fails again when trying to remove files), or a mocked test could be used instead (which would return this result).