fix: apply default revision when creating debugsession

[DinoChiesa]

The helpfile for creating a debugsession

   apigeecli apis debugsessions create --help

...states that the revision will default to "-1". This is true but not helpful, as the --rev option is marked as required. Therefore this command won't succeed:

apigeecli apis debugsessions create --name $APIPROXY --env $ENV

This change actually uses the latest revision when no --rev flag is present.

Also a similar change for the apis/debugsessions/get command:

apigeecli apis debugsessions get --ses ${SESSIONID} --name $APIPROXY --env $ENV

And for the apis/undeploy command:

apigeecli apis undeploy --name $APIPROXY --env $ENV