When operator needs to change any options described in sshd_config,
he/she should use the parameter named SshServerOptions to define
the updated configuration.
However the problem here is that he/she should define the whole content
instead of the actual lines to be overridden, otherwise some of the
lines defined in its default can be missing from configuration. This
makes it difficutlt to properly update the parameter during update or
upgrade, since operators always need to check whetehr any change has
been made about the default of SshServerOptions.
This change introduces a new parameter, SshServerOptionsOverride, which
can be used to override specific line in SshServerOptions. Note that
SshServerOptions should still be used if any of the lines in
SshServerOptions needs to be removed.
Change-Id: I8a018c8c7435a753c8ed5b5fa211d91d053f8d67
bfd97da0bf