Fix anti-affinity server-group boot failure

When the second instance is booted to an anti-affinity group
the scheduler fails with an exception due to a missing type conversion.

Closes-Bug: #1301982
Change-Id: I87b2a8d8c7d04b781c789374d6e9c7f4c8567e5d
(cherry picked from commit 1680cf8cef9bd670306a0ef74803409f60f21f28)
Merge "Fix anti-affinity server-group boot failure" into milestone-proposed