Move the Samba log depot validation code from LogFile.verify_log_depot_settings into FileDepotSmb.validate.

https://bugzilla.redhat.com/show_bug.cgi?id=1151173
Change the signature of FileDepotFtp#connect and #with_connect

to allow passing a hash of username and password so that depot can be validated without creating a record in DB.

https://bugzilla.redhat.com/show_bug.cgi?id=1151173
Add FileDepotFtp.validate for depot validation.

https://bugzilla.redhat.com/show_bug.cgi?id=1151173
Delete method LogFile.verify_log_depot_settings.

Currently this method works only for Samba depot validation.
The validation logic for Samba has been moved into FileDepotSmb.validate.
Logic for Ftp depot validation has been added into FileDepotFtp.validate.
The other two depot type, Anonymous FTP and NFS, don't require credentials.

https://bugzilla.redhat.com/show_bug.cgi?id=1151173
Delete unused method LogFile.validate_log_depot_settings.

https://bugzilla.redhat.com/show_bug.cgi?id=1151173
Use the new method to validate log depots.

https://bugzilla.redhat.com/show_bug.cgi?id=1151173
Merge pull request #908 from lfu/ftp_log_depot_validate_1151173

Fix the issue with defining FTP log depot.