https://build.spring.io/browse/INT-MASTER-1481
The `SftpSession.connect()` may lead to race condition when we try to
open the `channel`, but `JschSession` is closed already.
It may happen in cases when we have `DefaultSftpSessionFactory`
configured for the `isSharedSession` and that shared session may be
closed by another thread before we reach the `channel.connect()`,
because we already have left the `this.sharedSessionLock` blocking path
**Cherry-pick to 5.1.x**
8aef55f061