Use Patroni API to set bootstrap-only options. (#299)

Call Patroni API /config in order to set special options that are
ignored when set in the configuration file, such as max_connections.
Per https://github.com/zalando-incubator/postgres-operator/issues/297

* Some minor refacoring:

Rename Cluster ManualFailover to Swithover
Rename Patroni Failover to Switchover
Add more details to error messages and comments introduced in this PR.

Review by @zerg-junior

pkg/spec/types.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"io/ioutil"
 	"log"
+	"os"
 	"strings"
 	"time"
 
@@ -14,6 +15,7 @@ import (
 	"k8s.io/client-go/pkg/apis/apps/v1beta1"
 	policyv1beta1 "k8s.io/client-go/pkg/apis/policy/v1beta1"
 	"k8s.io/client-go/rest"
+
 )
 
 // EventType contains type of the events for the TPRs and Pods received from Kubernetes
@@ -223,6 +225,9 @@ func (r RoleOrigin) String() string {
 // Placing this func here instead of pgk/util avoids circular import
 func GetOperatorNamespace() string {
 	if operatorNamespace == "" {
+		if namespaceFromEnvironment := os.Getenv("OPERATOR_NAMESPACE"); namespaceFromEnvironment != "" {
+			return namespaceFromEnvironment
+		}
 		operatorNamespaceBytes, err := ioutil.ReadFile(fileWithNamespace)
 		if err != nil {
 			log.Fatalf("Unable to detect operator namespace from within its pod due to: %v", err)