tests: Fix broken targets check-report-qtest-*

They need QTEST_QEMU_IMG. Without it, the tests raise an assertion:

$ make -C bin check-report-qtest-i386.xml
make: Entering directory 'bin'
GTESTER check-report-qtest-i386.xml
blkdebug: Suspended request 'A'
blkdebug: Resuming request 'A'
ahci-test: tests/libqos/libqos.c:162:
 mkimg: Assertion `qemu_img_path' failed.
main-loop: WARNING: I/O thread spun for 1000 iterations

Signed-off-by: Stefan Weil <sw@weilnetz.de>
Reviewed-by: John Snow <jsnow@redhat.com>
Message-id: 1437231284-17455-1-git-send-email-sw@weilnetz.de
Signed-off-by: John Snow <jsnow@redhat.com>
