fix(ha): clear stale ha_failed when refreshing HA active state

[krystian-elisity]

Problem

PanDevice.refresh_ha_active() refreshes each device's _ha_active flag from
the live HA state, but it never clears ha_failed. A device that was marked
failed by a prior transient connection error (via set_failed()) therefore
stays "failed" even after it has recovered and is reachable again.

Because XapiWrapper routes API calls away from a device whose ha_failed is
True (to the HA peer), calls keep going to the peer indefinitely. In a
Panorama HA pair this means User-ID / config calls are sent to the passive
member, which silently never propagates them to the firewalls.

Root cause

refresh_ha_active() only reaches its else branch after successfully reading
the live HA state from both devices (show_highavailability_state()). A
successful read proves the device is reachable, so ha_failed should be cleared
there — but the method only updated _ha_active, leaving the stale ha_failed
behind. There was no path (other than manual dev.ha_failed = False or
set_failed() on the peer) to recover routing.

Fix

Clear ha_failed for each device whose live HA state was successfully read,
alongside the existing _ha_active update. Non-authoritative states
(disabled / initial) return early, so the flag is left untouched when the
state is not trustworthy.

else:
    for fw, state in ((self, self_state), (self.ha_peer, peer_state)):
        fw._ha_active = state == "active"
        # Reached this device for its state, so it is no longer failed.
        fw.ha_failed = False
    return self_state

Tests

Adds TestFirewallHa covering both paths:

• test_refresh_ha_active_clears_stale_ha_failed — a live refresh clears
  ha_failed on the reachable device.
• test_refresh_ha_active_keeps_ha_failed_when_state_not_authoritative — a
  non-authoritative (initial / disabled) state leaves ha_failed untouched.

Compatibility

No API change. refresh_ha_active() keeps its signature and return value; it
just additionally clears the stale flag it was always meant to reconcile.