Allow retrying connecting SshSession in case of an exception

Allow retrying connecting SshSession in case of an exception

Connecting to an SshSession may fail due to different reasons. Jsch for
example often throws an com.jcraft.jsch.JschException: verify: false.[1]
The issue is still not fixed in JSch 0.1.51.

In such a case it is worth retrying to connect. The number of connection
attempts can be configured using ssh_config parameter
"ConnectionAttempts" [2].

Don't retry if the user canceled authentication.

[1] http://sourceforge.net/p/jsch/bugs/58/
[2] http://linux.die.net/man/5/ssh_config

Bug: 437656
Change-Id: I6dd2a3786b7d3f15f5a46821d8edac987a57e381
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>