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
CP-5817: Productise removal of lvm2-environment-device.patch

Part of the change for rolling back lvm2-environment-device.patch. Removed code
that exports special environment variable to direct LVM to look for an
abbreviated device cache.

The second part of the change (actual removal of lvm patch) is under
guest-packages.

Signed-off-by: Chandrikas Srinivasan <chandrika.srinivasan@citrix.com>
Reviewed-by: Zheng Li <zheng.li@eu.citrix.com>

Github: close #28 on xapi-project/sm