This change corrects a few logging issues:
* Standardized formatting errors with '%v'.
* Standardized failure warning word usage.
* Corrected an instance of using the standard log library when
the gitea log library should be used instead.
When use builtin SSH server with concurrent operations, there are probabilities
One connection could use the command from another connections.
Fix this by set SSH_ORIGINAL_COMMAND for each command, not set in global scope.
According to the docs [1], the Reply method must be called for all
requests where WantReply is true. This fixes a hanging java ssh
implementation (jsch) which sets WantReply flag and waits for reply from
the server.
[1] https://godoc.org/golang.org/x/crypto/ssh#Request.Reply
