playbook_sysupgrade: fix fatal error on local connections

issuing a "sysupgrade" through a jumphost makes ansible raise an
"unrechable" error.

issuing a "sysupgrade" through a direct connection makes ansible raise
an "fatal" error.

Because the latter case was not properly delt with the playbook aborted
for that specific device. This commit fixes this problem.

playbook_sysupgrade.yml

@@ -31,6 +31,7 @@
           shell:
             cmd: "sysupgrade /tmp/{{ firmware_file | basename }} && exit 0"
           ignore_unreachable: yes
+          ignore_errors: yes
 
         - name: wait till device is back online
           wait_for_connection: