Description of problem:
Summary graph line will drop to 0 in between two collection point although metrics value is constant and not equal to 0. 

Version-Release number of selected component (if applicable):
RHQ 4.12

How reproducible:
Always

Steps to Reproduce:
1. Add to inventory RHQ Server resource (if it's not added already);
2. From RHQ UI -> navigate to JBossAS7 Standalone Servers -> RHQ Server resource -> Subsystems -> Connector -> datasources -> DataSource(Standalone) -> Monitoring -> Schedule
3. Change Max Pool Size collection period from 4h to 20 minutes;
4. After an hour, navigate to DataSource(Standalone) resource -> Monitoring -> Metrics -> and click on Max Pool Size to open a graph


Actual results:
Summary graph line is represented with spikes at the collection points but then this line will drop to 0 although the value of this metric is constant and equal 5 by default.

Expected results:
Graph that clearly shows metric value at the collection point and maybe a dotted line in between two collection points (that would show there was no other collections in between).

The other suggestions for the graph:

a) a bar at the measurement time (JON does this on other graphs)
b) a simple dot at the measurement time, no connecting lines
c) a dot at the measurement time, dots are connected with a line but the dot is so large that is clear that the line is based on these dots and no other measurements support the line