PHOENIX-1466 Prevent multiple scans when query run serially

Conflicts:
	phoenix-core/src/main/java/org/apache/phoenix/execute/ScanPlan.java
	phoenix-core/src/main/java/org/apache/phoenix/iterate/SerialIterators.java
	phoenix-core/src/main/java/org/apache/phoenix/iterate/TableResultIterator.java

Conflicts:
	phoenix-core/src/main/java/org/apache/phoenix/expression/aggregator/DistinctValueWithCountServerAggregator.java
PHOENIX-1463 phoenix.query.timeoutMs doesn't work as expected (Samarth Jain)