vmwareapi: remove unused update_host_status method

The VMWare driver declares a method 'update_host_status'
which has no callers anywhere in the codebase.

This is left over code that was missed in the cleanup from

  commit 2cb47fbabf09ced76178e8453d508c66f86a7a3a
  Author: Arata Notsu <notsu@virtualtech.jp>
  Date:   Thu Oct 18 22:40:01 2012 +0900

    Remove ComputeDriver.update_host_status()

Partial-bug: #1333219
Change-Id: Ie0de9b6d427246cb3c3adb818d483b61dfb08d82
Avoid re-adding iptables rules for instances that have disappeared

The remove_filters_for_instance() method fails silently if the
instance's chain is gone (i.e. it's been deleted). If this
happens while we're refreshing security group rules, we will
not notice this case and re-add stale rules for an old instance,
breaking our firewall for new instances.

This adds a quick check after we've captured the lock to see if
the associated chain exists, and bails if it doesn't.

Change-Id: Ic75988939f82de49735d85fe99a9eecd4baf45c9
Related-bug: #1182131
Merge "vmwareapi: remove unused update_host_status method"
Merge "Avoid re-adding iptables rules for instances that have disappeared"