CP-5330: Replace open-iscsi-auth.patch with discoverydb solution

This is part of the CP-5330 work to get rid of our customized patches
against open-iscsi and to use the stock version open-iscsi of upstream.
This changset replace open-iscsi-auth.patch with the mechanics provided
by the discoverydb mode, to allow CHAP authentication while doing iscsi
targets discovery.

Signed-off-by: Zheng Li <zheng.li@eu.citrix.com>
Suggested-by: Robert Breker <robert.breker@citrix.com>
Reviewed-by: Germano Percossi <germano.percossi@citrix.com>
CP-5330: Remove dependencies on iscsid-mpath.conf/iscsid-default.conf

This is part of the CP-5330 work to get rid of our customized patches
against open-iscsi and to use the stock version open-iscsi of upstream.

Previously we ship two customized versions of /etc/iscsi.conf only for
the purpose of switching one single configuration variable:
"replacement_timeout" (depending on whether multipath is enabled or not).

This is overkilled, and demand us to ship a customized build of open-iscsi.
As suggested by @robertbreker, the same effect can be possibly archived
by tweaking timeouts in the multipath layer, namely dev_loss_cmo etc.,
which we've already done in our multipath package.

This is a patch to remove SM's dependency on iscsi-mpath.conf and
iscsi-default.conf. One can still make use of them optionally by
manually creating these two files. This is useful if a customer still
needs a customized setting for some reason or for debugging purpose,
and the code is also backward compatible this way.

Signed-off-by: Zheng Li <zheng.li@eu.citrix.com>
Suggested-by: Robert Breker <robert.breker@citrix.com>
Reviewed-by: Germano Percossi <germano.percossi@citrix.com>
CP-5330: Dynamic set replacement_timeout during iscsi session establishment

Instead of linking/patching iscsid.conf statically, we now set
replacement_timeout dynamically whenever we establish a new iscsi session. As
part of the CP-5330 effort, this helps us to avoid monkey patching the upstream
open-iscsi.

Signed-off-by: Zheng Li <zheng.li@eu.citrix.com>
Suggested-by: Robert Breker <robert.breker@citrix.com>
Reviewed-by: Germano Percossi <germano.percossi@citrix.com>
Merge changes for CP-5330

GitHub: closes #25 on xapi-project/sm