configure: Enable out-of-tree acceptance tests

Currently to run Avocado acceptance tests in an out-of-tree
build directory, we need to use the full path to the test:

  build_dir$ avocado run /full/path/to/sources/qemu/tests/acceptance/boot_linux_console.py

This patch adds a symlink in the build tree to simplify the
tests invocation, allowing the same command than in in-tree builds:

  build_dir$ avocado run tests/acceptance/boot_linux_console.py
Signed-off-by: NPhilippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20180612173437.14462-1-f4bug@amsat.org>
Signed-off-by: NEduardo Habkost <ehabkost@redhat.com>

configure

@@ -7239,9 +7239,11 @@ for rom in seabios vgabios ; do
 done
 
 # set up tests data directory
-if [ ! -e tests/data ]; then
-    symlink "$source_path/tests/data" tests/data
-fi
+for tests_subdir in acceptance data; do
+    if [ ! -e tests/$tests_subdir ]; then
+        symlink "$source_path/tests/$tests_subdir" tests/$tests_subdir
+    fi
+done
 
 # set up qemu-iotests in this build directory
 iotests_common_env="tests/qemu-iotests/common.env"