dispatch _configure_aparams in PlatformAgent so the alert definitions are captured and processed

Fixes https://jira.oceanobservatories.org/tasks/browse/OOIION-1268

UI testing using

    bin/pycc -x ion.processes.bootstrap.ion_loader.IONLoader op=load  scenario=BETA,R2_DEMO loadui=True attachments=res/preload/r2_ioc/attachments ui_path="https://userexperience.oceanobservatories.org/database-exports/Candidates"  path=master

In the UI adding the following alert def to the "Beta Demonstration Platform Device" platform:

    {"stream_name":     "parsed",
     "alert_type":      1,   
     "name":            "input_voltage_warning_interval",
     "lower_bound":     111,
     "aggregate_type":  2,
     "alert_class":     "IntervalAlert",
     "value_id":        "input_voltage",
     "lower_rel_op":    "<",
     "description":     "input_voltage is below the normal range of 111 and above."}  

Then after putting the platform in monitoring state I can see the alerts being processed in the logs and also the corresponding "data" status icon changing color upon refresh of the page.

Integration tests:

The existing integration test test-alerts in:
   https://github.com/ooici/coi-services/blob/master/ion/agents/platform/test/test_platform_agent_with_rsn.py
was adjusted to also test alert defs passed via configuration to the platform agent.

NOTE: The base class calls _configure_aparams as part of on_init, but the PlatformAgent currently does much of its preparations in on_start, including the set-up of the alert manager and the status manager. So, as a mechanism to handle this, we basically save the argument `aparams` for actual processing during on_start.