Add delay and duration parameters for the JFR telemetry device #1617
Description
The JFR telemetry device while very useful, currently, only captures flight recordings from the time that ES starts until it's been stopped. This makes it hard to grab more focused JFRs for specific tasks, e.g. the scroll task in http_logs.
The current workaround is to leverage include|exclude tasks to reduce the amount of operations but often it's not an option as indexing usually needs to take place anyway and also skipping preceding tasks tends to affect reproducability.
Until we get a way to coordinate tasks and telemetry device execution in Rally, a short-term improvement could be allowing to pass the delay and duration parameters to jcmd, as per the official jcmd docs for JFR.start. Currently we only support one parameter (recording-template) for the jfr telemetry device, and adding those two should be a straightforward task.