Fix usage of array for X Axis in chart

In case of multi-block the array name were wrong as we were
using the serie name that contains the block full path.

Extend API to either get the Array list or the serie list.
Change the SI class implementation to get the array name
instead of the serie name.

Change-Id: Iee13cdb7426184ce6d49ac26b8fa1b9e45c2df23
Merge topic 'multiblock-chart-array-as-axis' into next

c87daf1 Fix usage of array for X Axis in chart