https://bugzilla.redhat.com/show_bug.cgi?id=1356436

According to RFC 3721 (https://www.ietf.org/rfc/rfc3721.txt), there are
two ways to "discover" targets in/for the iSCSI environment. Discovery
is the process which allows the initiator to find the targets to which
it has access and at least one address at which each target may be
accessed.

The method currently implemented in libvirt using the virISCSIScanTargets
API is known as "SendTargets" discovery. This method is more useful when
the target IP Address and TCP port information are available, e.g. in
libvirt terms the "portal". It returns a list of targets for the portal.
From that list, the target can be found. This operation can also fill an
iSCSI node table into which iSCSI logins may occur. Commit id '56057900'
altered that filling by adding the "--op nonpersistent" since it was
not necessarily desired to perform that for non libvirt related targets.

The second method is "Static Configuration". This method not only needs
the IP Address and TCP port (e.g. portal), but also the iSCSI target name.
In libvirt terms this would be the device path field from the iSCSI pool
<source> XML. This patch implements the second methodology using that
required device path as the targetname.

No longer necessary to have it, so remove it.

https://bugzilla.redhat.com/show_bug.cgi?id=1331552

Instead of disabling auto-login of all scsi targets (even those
that do not "belong" to libvirt), use iscsiadm's "--op nonpersistent"
during discovery of iSCSI targets (e.g. "iscsiadm --mode discovery
--type sendtargets") in order to avoid the node database being altered
which led to the need for the "large hammer" approach taken by
commit id '3c12b654'.

This commit removes the virISCSITargetAutologin adjustment (eg. the setting
of node.startup to "manual"). The iscsiadm command has supported this mode
of operation as of commit id 'ad873767' to open-iscsi.

Utilize the exit status parameter for virCommandRunRegex in order to
check the return error from the 'iscsiadm --mode session' command.
Without this enabled, if there are no sessions running then virCommandRun
would have displayed an error such as:

    2016-05-13 15:17:15.165+0000: 10920: error : virCommandWait:2553 :
               internal error: Child process (iscsiadm --mode session)
               unexpected exit status 21: iscsiadm: No active sessions.

It is possible that for certain paths (when probe is true) we only care
whether it's running or not to make certain decisions.  Spitting out
the error for those paths is unnecessary.

If we do have a situation where probe = false and there's an error,
then display the error from iscsiadm if it's there.

Rather than have virCommandRun just spit out the error, allow callers
to decide to pass the exitstatus so the caller can make intelligent
decisions based on the error.

https://bugzilla.redhat.com/show_bug.cgi?id=1172015

The refactoring done as part of commit id '59446096' caused a regression
for the multi initiator IQN commit '6aabcb5b' because the sendtargets was
not done on/for the initiator IQN prior to login (or trying to disable
autologin)

Prior to that commit, the paths were essentially

virStorageBackendISCSIStartPool
    virStorageBackendISCSILogin
        virStorageBackendISCSIConnection
            if initiatoriqn
                virStorageBackendCreateIfaceIQN
                Issue sendtargets
                Perform --login
            else
                Issue sendtargets
                Perform --login

After that commit:

virStorageBackendISCSIStartPool
    Issue sendtargets
    Call virStorageBackendISCSIConnection
        If initiatoriqn
            virStorageBackendCreateIfaceIQN
            Perform --login
        else
            Perform --login

So for non initiator IQN paths, nothing changed. For the initiator path,
the --login fails as does any attempts to change autologin via "--op update
--name node.startup --value manual".

Signed-off-by: NMartin Kletzander <mkletzan@redhat.com>

Remove the 'StorageBackend' from names of the functions and fix
indentation.