restapi : list files with --max issue

List files wth --max parameter retrieves extra results
if the ISO domain has both .iso and .vfd files.

This patch comines the two into 1 query so that the
max number of results is the same as specfied by
--max

Change-Id: I7cf453d430f44dff8725ea11ecc0fa91d99844bc
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=886794
Signed-off-by: Ravi Nori <rnori@redhat.com>