Fix to use correct config options for ping_timeout
Fix to use correct config options for ping_timeout

ping_timeout config options under compute group have been
deprecated since 1 year and it has been under new group validation.

Tempest will remove the deprecated config options soon.

This commit use the config options from correct group.

Change-Id: I1b1fa234969fafe13940384b54a9517de60ad3da

stackforge/gce-api,stackforge/gce-api