kola/tests/update: increase update timeout for arm64

[pothos]

The 2 minute timeout was too short on arm64 qemu emulation for
completing the update.
Increase the timeout to 10 minutes.

How to use/testing done

sudo ./kola run --board=arm64-usr --channel=alpha --platform=qemu  --update-payload=tmp/flatcar_test_update.gz --qemu-bios=tmp/flatcar_production_qemu_uefi_efi_code.fd --qemu-image=tmp/flatcar_production_image.bin cl.update.payload
=== RUN   cl.update.payload
--- PASS: cl.update.payload (1032.33s)
        cluster.go:117: Created symlink /etc/systemd/system/locksmithd.service → /dev/null.
        update.go:149: Triggering update_engine
        update.go:168: Rebooting test machine
        update.go:149: Triggering update_engine
        update.go:168: Rebooting test machine
PASS, output in _kola_temp/qemu-2021-07-14-1931-2822851