Upgrade Palo Firewalls (CLI)

Steps:
0. Confirm firewalls are in sync and turn preemption off on both
1. Failover to Secondary
2. Install 8.1.6 on Primary
3. Reboot Primary
4. Login and check if 8.1.6 is installed on Primary and then failback to Primary
5. Check traffic going through Primary
6. Install and reboot 8.1.6 for Secondary
7. Login and check if 8.1.6 is installed on Secondary
8. Turn preemption on both

Useful commands:
request system software info
request system software check
request system software download version 8.1.6
request restart system
delete software version 8.1.6

show high-availability state

request system software install version 8.1.6
request high-availability state suspend
request high-availability state functional
request high-availability sync-to-remote
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