oeqa ssh.py: add connection keep alive options to ssh client

oeqa ssh.py: add connection keep alive options to ssh client

Configure ssh client to test that connection with server is up.
If the server does not respond within a minute then the connection,
target machine or sshd daemon are stuck and it's better to exit
the command execution with errors.

Some tests can execute a long time without returning stdout/stderror
data and it's difficult to adjust timers for those cases if
connection to target machine or the target machine itself hangs
and output is not expected in minutes or even hours.

Signed-off-by: Mikko Rapeli <mikko.rapeli@linaro.org>
Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
(cherry picked from commit ba68ff04c5786eca7cd8dd44056705867dea8ac4)
Signed-off-by: Steve Sakoman <steve@sakoman.com>