Fixes unexpected exception message in PciConfigInvalidWhitelist

When an exception PciConfigInvalidWhitelist occurs, the message "An
unknown exception occurred." was obtained. This is due to the content
of the variable not being overriden correctly. The same typo applies
to PciTrackerInvalidNodeId.

Closes-Bug: #1221493
Change-Id: I589cb8d0a1426eb84bbbc4a819b5585e4e746843
Merge "Fixes unexpected exception message in PciConfigInvalidWhitelist"