iotests: Set LC_ALL=C for sort

Otherwise the result is basically unpredictable.

(Note that the precise environment variable to control sorting order is
LC_COLLATE, but LC_ALL overrides LC_COLLATE, and we do not want the
sorting order to be messed up if LC_ALL is set in the environment.)

Reported-by: John Snow <jsnow@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20200710163253.381630-3-mreitz@redhat.com>

tests/qemu-iotests/common.filter

@@ -186,7 +186,7 @@ _filter_img_create()
             -e 's/^\(data_file\)/3-\1/' \
             -e 's/^\(encryption\)/4-\1/' \
             -e 's/^\(preallocation\)/8-\1/' \
-        | sort \
+        | LC_ALL=C sort \
         | $SED -e 's/^[0-9]-//' \
         | tr '\n\0' ' \n' \
         | $SED -e 's/^ *$//' -e 's/ *$//'