iotests: Fix 195 if IMGFMT is part of TEST_DIR

iotests: Fix 195 if IMGFMT is part of TEST_DIR

do_run_qemu() in iotest 195 first applies _filter_imgfmt when printing
qemu's command line and _filter_testdir only afterwards.  Therefore, if
the image format is part of the test directory path, _filter_testdir
will no longer apply and the actual output will differ from the
reference output even in case of success.

For example, TEST_DIR might be "/tmp/test-qcow2", in which case
_filter_imgfmt first transforms this to "/tmp/test-IMGFMT" which is no
longer recognized as the TEST_DIR by _filter_testdir.

Fix this by not applying _filter_imgfmt in do_run_qemu() but in
run_qemu() instead, and only after _filter_testdir.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Message-id: 20170927211334.3988-1-mreitz@redhat.com
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>