Move stream template to batch implementation

I have a lot of tasks running that use a stream template. When I changed that stream template to fix some minor bugs, tasks were correctly updated to use the new template when restarted.

However when I tried to move the stream template to a batch implementation, kapacitor did not want to restart and gave me the following error:

> run: open server: failed to reload tasks/templates/handlers: failed to load file /opt/kapacitor/templates/sensor_boolean.tick: failed to create template: invalid TICKscript: name "batch" is undefined. Names in scope: time,stream,sensorId,alertDefinitionId,criticalValue

Looks like kapacitor does not allow moving from a stream template implementation to a batch template implementation. Is this a feature that is under consideration?

My workaround will be redefining all my tasks with the new batch-based template (which will live under a different name than the stream template). But this is hardly an ideal situation.

Start with the template reload path identified by tasks/templates/handlers and reproduce the failure using /opt/kapacitor/templates/sensor_boolean.tick, which currently reports an undefined batch name in TICKscript. Done means an existing task can be restarted after its template changes from stream to batch without requiring a separately named template.

Written by the indexing model from the issue text.