JIRA: https://jira.spring.io/browse/INT-4175
Fixes GH-1980 (https://github.com/spring-projects/spring-integration/issues/1980)
When the `isSharedSession` is used for the `DefaultSftpSessionFactory`,
there is some race condition window when we can call the target `this.jschSession.connect()` several times and end up with the session is already connected.
Wrap `sftpSession.connect()` to the `this.sharedSessionLock.readLock().lock()` when `isSharedSession` to protect from that race condition.
Note: there is no test for this change because it is pretty tricky to build barriers between threads for this kind of race conditions.
Especially after introduction `this.sharedSessionLock.readLock().lock()` around guilty code
**Cherry-pick to 4.3.x & 4.2.x**
Move `sharedJschSession` connect logic to the existing locking block
Fix mock test to reflect the current ConnectionFactory state
85730bfe60