Handle DELETED files . Add support for inode changes ( for the same file )

1. Check /proc/self/fd/ directory and stop harvesting file it it was deleted 

2. Introduced  new configuration  option , rsync . 
 "fields": {  "rsync": "yes" }
We rsync files from remote location and rsync changes inode numbers for some of the files . 
The content of the files is still the same , so we should continue to harvest them .
By default logstash-forwarder will stop harvesting files on inode change .