Kubernetes Mesos integration

This commit includes the fundamental components of the Kubernetes Mesos
integration:

* Kubernetes-Mesos scheduler
* Kubernetes-Mesos executor
* Supporting libs

Dependencies and upstream changes are included in a separate commit for easy
review.

After this initial upstream, there'll be two PRs following.

* km (hypercube) and k8sm-controller-manager #9265
* Static pods support #9077

Fixes applied:

- Precise metrics subsystems definitions
  -  mesosphere/kubernetes-mesos#331
  - https://github.com/GoogleCloudPlatform/kubernetes/pull/8882#discussion_r31875232
  - https://github.com/GoogleCloudPlatform/kubernetes/pull/8882#discussion_r31875240
- Improve comments and add clarifications
  - Fixes https://github.com/GoogleCloudPlatform/kubernetes/pull/8882#discussion-diff-31875208
  - Fixes https://github.com/GoogleCloudPlatform/kubernetes/pull/8882#discussion-diff-31875226
  - Fixes https://github.com/GoogleCloudPlatform/kubernetes/pull/8882#discussion-diff-31875227
  - Fixes https://github.com/GoogleCloudPlatform/kubernetes/pull/8882#discussion-diff-31875228
  - Fixes https://github.com/GoogleCloudPlatform/kubernetes/pull/8882#discussion-diff-31875239
  - Fixes https://github.com/GoogleCloudPlatform/kubernetes/pull/8882#discussion-diff-31875243
  - Fixes https://github.com/GoogleCloudPlatform/kubernetes/pull/8882#discussion-diff-31875234
  - Fixes https://github.com/GoogleCloudPlatform/kubernetes/pull/8882#discussion-diff-31875256
  - Fixes https://github.com/GoogleCloudPlatform/kubernetes/pull/8882#discussion-diff-31875255
  - Fixes https://github.com/GoogleCloudPlatform/kubernetes/pull/8882#discussion-diff-31875251
- Clarify which Schedule function is actually called
  - Fixes https://github.com/GoogleCloudPlatform/kubernetes/pull/8882#discussion-diff-31875246

contrib/mesos/pkg/scheduler/constraint/constraint.go

@@ -0,0 +1,106 @@
+/*
+Copyright 2015 The Kubernetes Authors All rights reserved.
+
+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 constraint
+
+import (
+	"encoding/json"
+	"fmt"
+)
+
+type OperatorType int
+
+const (
+	UniqueOperator OperatorType = iota
+	LikeOperator
+	ClusterOperator
+	GroupByOperator
+	UnlikeOperator
+)
+
+var (
+	labels = []string{
+		"UNIQUE",
+		"LIKE",
+		"CLUSTER",
+		"GROUP_BY",
+		"UNLIKE",
+	}
+
+	labelToType map[string]OperatorType
+)
+
+func init() {
+	labelToType = make(map[string]OperatorType)
+	for i, s := range labels {
+		labelToType[s] = OperatorType(i)
+	}
+}
+
+func (t OperatorType) String() string {
+	switch t {
+	case UniqueOperator, LikeOperator, ClusterOperator, GroupByOperator, UnlikeOperator:
+		return labels[int(t)]
+	default:
+		panic(fmt.Sprintf("unrecognized operator type: %d", int(t)))
+	}
+}
+
+func parseOperatorType(s string) (OperatorType, error) {
+	t, found := labelToType[s]
+	if !found {
+		return UniqueOperator, fmt.Errorf("unrecognized operator %q", s)
+	}
+	return t, nil
+}
+
+type Constraint struct {
+	Field    string       // required
+	Operator OperatorType // required
+	Value    string       // optional
+}
+
+func (c *Constraint) MarshalJSON() ([]byte, error) {
+	var a []string
+	if c != nil {
+		if c.Value != "" {
+			a = append(a, c.Field, c.Operator.String(), c.Value)
+		} else {
+			a = append(a, c.Field, c.Operator.String())
+		}
+	}
+	return json.Marshal(a)
+}
+
+func (c *Constraint) UnmarshalJSON(buf []byte) (err error) {
+	var a []string
+	if err = json.Unmarshal(buf, &a); err != nil {
+		return err
+	}
+	switch x := len(a); {
+	case x < 2:
+		err = fmt.Errorf("not enough arguments to form constraint")
+	case x > 3:
+		err = fmt.Errorf("too many arguments to form constraint")
+	case x == 3:
+		c.Value = a[2]
+		fallthrough
+	case x == 2:
+		c.Field = a[0]
+		c.Operator, err = parseOperatorType(a[1])
+	}
+	return err
+}