Cleanup orchestration documents (#5623)

- Remove hostPort from Kubernetes deployment example docs. Initially
hostPort was added to ensure Minio pods are allocated to separate
machines, but as per latest Kubernetes documents this is not
recommended approach (ref: https://kubernetes.io/docs/concepts/
configuration/overview/#services). To define pod allocations,
Affinity and Anti-Affinity concepts are the recommended approach.
(ref: https://kubernetes.io/docs/concepts/configuration/assign-pod-node)

- Add Minio release tag to Docker-Compose example file.

docs/orchestration/docker-compose/docker-compose.yaml

@@ -5,7 +5,7 @@ version: '2'
 # 9001 through 9004.
 services:
  minio1:
-  image: minio/minio
+  image: minio/minio:RELEASE.2018-02-09T22-40-05Z
   volumes:
    - data1:/data
   ports:
@@ -15,7 +15,7 @@ services:
    MINIO_SECRET_KEY: minio123
   command: server http://minio1/data http://minio2/data http://minio3/data http://minio4/data 
  minio2:
-  image: minio/minio
+  image: minio/minio:RELEASE.2018-02-09T22-40-05Z
   volumes:
    - data2:/data
   ports:
@@ -25,7 +25,7 @@ services:
    MINIO_SECRET_KEY: minio123
   command: server http://minio1/data http://minio2/data http://minio3/data http://minio4/data 
  minio3:
-  image: minio/minio
+  image: minio/minio:RELEASE.2018-02-09T22-40-05Z
   volumes:
    - data3:/data
   ports:
@@ -35,7 +35,7 @@ services:
    MINIO_SECRET_KEY: minio123
   command: server http://minio1/data http://minio2/data http://minio3/data http://minio4/data 
  minio4:
-  image: minio/minio
+  image: minio/minio:RELEASE.2018-02-09T22-40-05Z
   volumes:
    - data4:/data
   ports: