Show "0" in UI if there is no real cores

Currently, if we have some node without real cores we will see next
string in UI:

    CPU: ? (1)

Since now, we will see "0" instead of "?"

    CPU: 0 (1)

Change-Id: I4d3dfad5f2a96b2d303797ff8e2dd594ad78b19c
Closes-Bug: #1382545
Merge "Show "0" in UI if there is no real cores"