Move scheduler code out of plugin directory.

This moves plugin/pkg/scheduler to pkg/scheduler and
plugin/cmd/kube-scheduler to cmd/kube-scheduler.

Bulk of the work was done with gomvpkg, except for kube-scheduler main
package.

pkg/scheduler/algorithm/priorities/balanced_resource_allocation.go

@@ -0,0 +1,61 @@
+/*
+Copyright 2016 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package priorities
+
+import (
+	"math"
+
+	schedulerapi "k8s.io/kubernetes/pkg/scheduler/api"
+	"k8s.io/kubernetes/pkg/scheduler/schedulercache"
+)
+
+var (
+	balanceResourcePriority = &ResourceAllocationPriority{"BalanceResourceAllocation", balancedResourceScorer}
+
+	// BalancedResourceAllocationMap favors nodes with balanced resource usage rate.
+	// BalancedResourceAllocationMap should **NOT** be used alone, and **MUST** be used together
+	// with LeastRequestedPriority. It calculates the difference between the cpu and memory fraction
+	// of capacity, and prioritizes the host based on how close the two metrics are to each other.
+	// Detail: score = 10 - abs(cpuFraction-memoryFraction)*10. The algorithm is partly inspired by:
+	// "Wei Huang et al. An Energy Efficient Virtual Machine Placement Algorithm with Balanced
+	// Resource Utilization"
+	BalancedResourceAllocationMap = balanceResourcePriority.PriorityMap
+)
+
+func balancedResourceScorer(requested, allocable *schedulercache.Resource) int64 {
+	cpuFraction := fractionOfCapacity(requested.MilliCPU, allocable.MilliCPU)
+	memoryFraction := fractionOfCapacity(requested.Memory, allocable.Memory)
+
+	if cpuFraction >= 1 || memoryFraction >= 1 {
+		// if requested >= capacity, the corresponding host should never be preferred.
+		return 0
+	}
+
+	// Upper and lower boundary of difference between cpuFraction and memoryFraction are -1 and 1
+	// respectively. Multilying the absolute value of the difference by 10 scales the value to
+	// 0-10 with 0 representing well balanced allocation and 10 poorly balanced. Subtracting it from
+	// 10 leads to the score which also scales from 0 to 10 while 10 representing well balanced.
+	diff := math.Abs(cpuFraction - memoryFraction)
+	return int64((1 - diff) * float64(schedulerapi.MaxPriority))
+}
+
+func fractionOfCapacity(requested, capacity int64) float64 {
+	if capacity == 0 {
+		return 1
+	}
+	return float64(requested) / float64(capacity)
+}