Remove unused variables from ensure_export()

Remove unused variables from ensure_export()

After introducing commit 9651f547147188645942466602c92cce06666483,
these three variables are obsolete in ensure_export().
By remaining these variable, ensure_export() fails to export
volumes after c-vol service is restart because the caller of
ensure_export() in lvm driver does not pass these variables.

- iscsi_name, volume_group, config

Main clean up is done by commit Ibfd1feefd72c43ef316b267e9d6645f2e67e2558.
This patch adds some tests for tgt, lio, and iser targets.
And also adds initialization of chap_auth_userid and chap_auth_password
in create_iscsi_target() because these variables might be referred
before definition.

Closes-bug: 1408121
Related-bug: 1408171
Change-Id: I8766eee33ae07fea71873809bfec37b8352c3a89