Add period input parameter to basic strategy

This patch set adds new period strategy input parameter
which allows allows to specify the time length of
statistic aggregation.

Partial-Bug: #1614021

Change-Id: I1a276206e5b2c05d8f94acdeb866c8822fa84f35

doc/source/strategies/basic-server-consolidation.rst

@@ -71,6 +71,9 @@ parameter              type   default Value description
                                             be tried by the strategy while
                                             searching for potential candidates.
                                             To remove the limit, set it to 0
+``period``             Number 7200          The time interval in seconds
+                                            for getting statistic aggregation
+                                            from metric data source
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 Efficacy Indicator