Merge "fs_mgr_overlayfs: Try "/system" and "/" when setting "/system" shared type"

    if (ret) {

        PERROR << "__mount(target=" << mount_point

               << ",flag=" << (shared_flag ? "MS_SHARED" : "MS_PRIVATE") << ")=" << ret;

        // If "/system" doesn't look like a mountpoint, retry with "/".

        if (errno == EINVAL && mount_point == "/system") {

            return fs_mgr_overlayfs_set_shared_mount("/", shared_flag);

        }

        return false;

    }

    return true;