Fix NVMe partition naming logic, and resolve GRUB kernel boot and systemd TTY path bugs on ARM64

- Replace custom partition wrappers with standard GCOS partutil.PartNumIntToString utility.
- Fix customizer repartition reboot loop on ARM64 builder VMs by dynamically resolving systemd last-run TTYPath based on architecture (/dev/ttyAMA2 on ARM64).
- Fix boot rescue shell hangs on ARM64 UEFI by checking and copying the missing vmlinuz.B kernel on the EFI partition.

Change-Id: I2223a29c23cc48e89f9325384839b1940db9558b
Reviewed-on: https://cos-review.googlesource.com/c/cos/tools/+/159704
Tested-by: He Gao <hegao@google.com>
Cloud-Build: 228075978874@cloudbuild.gserviceaccount.com <228075978874@cloudbuild.gserviceaccount.com>
Reviewed-by: He Gao <hegao@google.com>