[PATCH] iotests: Work around failing readlink -f

[Max Reitz]

On macOS, (out of the box) readlink does not have -f.  If the recent
"readlink -f" call introduced by b1cbc33a397 fails, just fall back to
the old behavior (which means you can run the iotests only from the
build tree, but that worked fine for six years, so it should be fine
still).

Keep any potential error message on stderr.  If users want to run the
iotests from outside the build tree, this may point them to what's wrong
(with their system).

Fixes: b1cbc33a3971b6bb005d5ac3569feae35a71de0f
       ("iotests: Allow running from different directory")
Reported-by: Claudio Fontana <cfontana@suse.de>
Reported-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>
---
Hi Thomas,

I thought this would be quicker than writing a witty response on whether
you or me should write this patch. O:)
---
 tests/qemu-iotests/check | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/tests/qemu-iotests/check b/tests/qemu-iotests/check
index e14a1f354d..75675e1a18 100755
--- a/tests/qemu-iotests/check
+++ b/tests/qemu-iotests/check
@@ -45,6 +45,10 @@ then
     fi
     source_iotests=$(cd "$source_iotests"; pwd) || _init_error "failed to 
enter source tree"
     build_iotests=$(readlink -f $(dirname "$0"))
+    if [ "$?" -ne 0 ]; then
+        # Perhaps -f is unsupported, revert to pre-b1cbc33a397 behavior
+        build_iotests=$PWD
+    fi
 else
     # called from the source tree
     source_iotests=$PWD
-- 
2.26.2