Move variable definitions near to where they are used

In LoadBalancer::reuseConnection(), if the condition
"$serverIndex === null || $refCount === null" is met,
then those variables will not be used. So only define
them when they will readlly be used.

Change-Id: Ifbd4131f40d3babe733b8723d0d29d39890bb309
Merge "Move variable definitions near to where they are used"