iotests: Different iterator behavior in Python 3

In Python 3, several functions now return iterators instead of lists.
This includes range(), items(), map(), and filter().  This means that if
we really want a list, we have to wrap those instances with list().  But
then again, the two instances where this is the case for map() and
filter(), there are shorter expressions which work without either
function.

On the other hand, sometimes we do just want an iterator, in which case
we have sometimes used xrange() and iteritems() which no longer exist in
Python 3.  Just change these calls to be range() and items(), works in
both Python 2 and 3, and is really what we want in 3 (which is what
matters).  But because it is so simple to do (and to find and remove
once we completely switch to Python 3), make range() be an alias for
xrange() in the two affected tests (044 and 163).

In one instance, we only wanted the first instance of the result of a
filter() call.  Instead of using next(filter()) which would work only in
Python 3, or list(filter())[0] which would work everywhere but is a bit
weird, this instance is changed to use a generator expression with a
next() wrapped around, which works both in 2.7 and 3.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Eduardo Habkost <ehabkost@redhat.com>
Reviewed-by: Cleber Rosa <crosa@redhat.com>
Message-Id: <20181022135307.14398-6-mreitz@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>

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