1. Implement ExecResult class and cover it by unit tests
2. Migrate SSHClient on it
ExecResult class implements automatic deserialization of ssh output
(stdout & stderrto string, yand shstring (7 lines max)
Standard data (exit code, command, stdout & stderr) also stored.
Also this objace allow 2 ways access to data
getattr (as normal object)
getitem (backward compatibilitests)
Later this class is planned to re-use for subprocess helper.
Blueprint: sshmanager-integration
Change-Id: I0e630dc898fb1b476b4d277ce3867ae3513d248f
104328efb9