Checks for presence of Hyper-V cpu metrics before accessing

Adds a default value if there are no cpu metrics to be retrieved.

Closes-Bug: 1249959
(cherry picked from commit f15e2cc9248c99e9b5c6b371ecce4f0ed49450cc)

Change-Id: I39513648ab25d46b2639b24a94e7344954ce3aeb
Merge "Checks for presence of Hyper-V cpu metrics before accessing" into stable/havana