ci: install-windows-updates fix get_windows_updates_remaining loop

It appears that the new(er) version of `govc` does not retain/return the
exit code of a process when checking `guest.ps`, so that if a process
that was `guest.start`'ed exits before the process can be checked the
resulting JSON response will not contain an exit code (or at least that
appears to be what is happening).

In stead of breaking out of the loop to check for remaining updates when
there is _any_ response, we now check to see if the response is null or
not.

Author: aramprice

ci/tasks/install-windows-updates/run.sh

@@ -90,7 +90,7 @@ run_powershell_command_with_logging 'Install-PackageProvider -Name NuGet -Minimu
 run_powershell_command_with_logging 'Install-Module -Name PSWindowsUpdate -MinimumVersion 2.1.0.1 -Force'
 
 updates_remaining=$(get_windows_updates_remaining)
-echo "Windows Updates to install: ${updates_remaining}" >&2
+echo "Initial Windows Updates to install: ${updates_remaining}" >&2
 
 while [[ ${updates_remaining} -ne 0 ]]; do
   set +e # ignore unreachable agent if the vm just went down for reboot
@@ -100,12 +100,12 @@ while [[ ${updates_remaining} -ne 0 ]]; do
   wait_for_vm_to_come_up
 
   updates_remaining=""
-  while [[ -z "${updates_remaining}" || "${updates_remaining}" == "null" ]] ; do
+  while [[ "${updates_remaining}" != "null" ]] ; do
     set +e # ignore failures here since the vmware tools agent may be down while updates are being applied
     updates_remaining=$(get_windows_updates_remaining)
     set -e
   done
-  echo "Updates remaining: ${updates_remaining}" >&2
+  echo "Remaining Windows Updates to install: ${updates_remaining}" >&2
 done
 
 remote_hotfix_log_path="C:\\hotfix.log"