Fix up the way we do iqn variable in unit test

A recent bug was reported when a developer was trying to work
with the iscsi target unit tests.  There were two problems discovered,
one of which has been addressed by the dependent patch of this commit
(https://review.openstack.org/#/c/68223/) which fixed the inconsistencies
in the string we used for iqn's in our test.

This patch addresses another issue that's somewhat related and was
exposed when the developer tried to use the "self.target_name" variable
instead of hard-coding the iqn's in the tests.

The problem is that the target_name variable uses an invalid format
for the iqn based on cinder-defaults.  It neglected to use the
volume_name prefix (in this case: "volume-").

This patch modifies the self.target_name variable to be more accurate
with what we would see in real usage, it also modifies the test to just
use this variable rather than hard coding it and running the risk of
having mismatches again in the future.

Change-Id: I392d423d5c0f58b7a21ee0c477609265002faa0c
Make sure report_interval is less than service_down_time

Services that inherit service.py/Service class would register
themselves to DB and then update stats periodically (every
report_interval second).  The consumer of this kind of information,
like scheduler or 'os-service' API extension, will consider a service
is 'up' (active) if last update from that service is not longer than
'service_down_time' ago.

The problem is if 'report_interval' was configured/provided greater
than 'service_down_time' by mistake, services would then be always
considered in 'down' state, which can result in unsuccesful placement
of volume create request for example.  This is what Bug #1255685 is
about.

In previous fix: https://review.openstack.org/#/c/60760/, a
configuration check helper function basic_config_check() was added
*wrongly* to WSGIService class instead of Service class.  This patch
moves the configuration check helper function and the check to the
right place to make sure 'report_interval' is less then
'service_down_time'.

Closes-bug #1255685

Change-Id: I14bd8c54e5ce20719844f437808ad98a011820de
Merge "Fix up the way we do iqn variable in unit test"