Retry

[sonots]

This possibly fixes several connection issues such as below:

(1) Could not write to

2016-03-14T09:10:37 [WARN]         org.apache.commons.vfs2.FileSystemException: Could not write to \"sftp://xxxx/xxxxx\".\n\tat
2016-03-14T09:10:37 [WARN]         com.google.common.base.Throwables.propagate(Throwables.java:160)\n\tat 
2016-03-14T09:10:37 [WARN]         org.embulk.output.sftp.SftpFileOutput.nextFile(SftpFileOutput.java:122)\n\tat
2016-03-14T09:10:37 [WARN]         org.embulk.spi.util.FileOutputOutputStream.nextFile(FileOutputOutputStream.java:34)\n\tat

I implemented retry for this.

(2) Possible write failure

I did not meet with this on the production, but it possibly can happen. Fixed to retry writing.

NOTE: Retry writing may produce data duplication, users should always check number of rows coming from input, and number of rows written into output. I advise that users do such check always even if they do not turn on retry feature.

(3) Could not close the output stream for file

2016-03-14T12:10:43 [WARN] Caused by: java.lang.RuntimeException: org.apache.commons.vfs2.FileSystemException: Could not close the output stream for file "xxxx.zip".
2016-03-14T12:10:43 [WARN] \tat com.google.common.base.Throwables.propagate(Throwables.java:160)
2016-03-14T12:10:43 [WARN] \tat org.embulk.output.sftp.SftpFileOutput.closeCurrentFile(SftpFileOutput.java:181)
2016-03-14T12:10:43 [WARN] \tat org.embulk.output.sftp.SftpFileOutput.close(SftpFileOutput.java:152)

InputStream may close OutputStream. We can simply ignore errors on closing if output stream or file are already closed.

Extra

I also added Vagrantfile so that example can easily be ran.

[civitaspo]

good! thx so much!!!!