Raise error when period with negative value

Based on current implement, when use launch below REST API:
GET http://10.1.0.175:8777/v2/meters/port/statistics?period=-1
The result will be 200 OK. No any error reports. This query
should not allow negative value setting but 400 error, and
prompts like this: "Period must be positive.". Just like
setting "Limit" to negative.

Fixes bug 1212159

Change-Id: I8d547fdf8faae2094b24c81da6b233b432bc99ae
Reinitialize pipeline manager for service restart

For central and compute agent, they need to reinitialize
pipeline manager for service restart.
It depends on blueprint service-restart of oslo-incubator and
blueprint cfg-reload-config-files of oslo.config.

Implements blueprint pollster-runtime-configuration

Change-Id: Icf2597392222d6d97b3dbfd7d48e5ac3b84b175e
Merge "Reinitialize pipeline manager for service restart"
Merge "Raise error when period with negative value"