[FIXES JENKINS-18214] create BasicSSHUserPrivateKey.FileOnMasterPrivateKeySource using private key path
Merge pull request #9 from ndeloof/master

[JENKINS-18214] fail to migrate legacy ssh-slaves private key
[maven-release-plugin] prepare release ssh-slaves-0.26
[maven-release-plugin] prepare for next development iteration
Eliminated pointless use of threads

StreamGobbler is an active buffering InputStream implementation. "active" because it has a thread that pumps the input stream, and "buffering", because it maintains an unbounded byte[] buffer that spools the data until it gets consumed.

This is both wasteful and harmful. Wasteful, because it uses two threads here (and one StreamGobbler is connected to a StreamCopyThread, making this a double-buffering. On systems that have a large # of slaves, this reduction in the total # of slaves is considerable.

This is harmful, because it eliminates the point of SSH window size control. If the master is under load, this will prevent the master from naturally throttle data that slaves are sending to it.
Eliminated the need for pumping stderr.

trilead-ssh2 build214-jenkins-3 has the ability to directly deliver
stdout/stderr data to OutputStream of our choice.

This version ships in Jenkins 1.521. This change allows us to take
advantage of this feature when we run with this version, and eliminates
the need for the stream pump thread.

On a large deployment, the thread saving would be considerable.
[maven-release-plugin] prepare release ssh-slaves-0.27
[maven-release-plugin] prepare for next development iteration
HOSTDEV-970 Found a suspect that overides credentials for the slave

We do not understand what's going on -- why we're losing the credentials
so we're adding logging and disabling the upgrade as we don't need it