public boolean tryPrefill() {
    return tryReserve(minimum);
  }
Should be called when prefilling connections to reach minimum connections. Caller should only
create a connection if this method returns {@code true}. If connection creation fails then
{@link #cancelTryPrefill} must be called to revert the count increase.

@return {@code true} if count was under minimum and we increased it, otherwise {@code false}.
geode-core/src/main/java/org/apache/geode/cache/client/internal/pooling/ConnectionAccounting.java