Merge "Adding wait for a device file before mount"

// wrapper to __mount() and expects a fully prepared fstab_rec,

// unlike fs_mgr_do_mount which does more things with avb / verity etc.

int fs_mgr_do_mount_one(const FstabEntry& entry, const std::string& mount_point) {

    // First check the filesystem if requested.

    if (entry.fs_mgr_flags.wait && !WaitForFile(entry.blk_device, 20s)) {

        LERROR << "Skipping mounting '" << entry.blk_device << "'";

    }

    // Run fsck if needed

    prepare_fs_for_mount(entry.blk_device, entry);