Increase session IPMI timeout in VBMC

The default IPMI session timeout is 1s. This is rather
low if you use oooq to deploy a big overcloud on a biggish
server. Let's increase this timeout by a large amount so
to give plenty of time to vbmc to operate.

With this change the ironic errors I observe from time to
time on my deployments are gone.

Change-Id: I37afb2e7d9e57405b1c34b413f8152bed97a344a

roles/undercloud-deploy/tasks/configure-vbmc.yml

@@ -31,6 +31,8 @@
       [log]
       logfile=/var/log/virtualbmc/virtualbmc.log
       debug=True
+      [ipmi]
+      session_timout=20
   become: true
 
 # the non_root_user id is not in the facts of the virthost when