[elasticsearch] use bash for keystore init container (elastic#1464)

This commit is a follow up of 167278e and is updating the keystore
initContainer to also use bash instead of sh. This is required for
Elasticsearch > 7.16.0 because the Docker image is now based on Ubuntu
instead of CentOS 8, and sh on Ubuntu isn't compatible with the
`if [[... -eq ... ]]` statements.

elasticsearch/templates/statefulset.yaml

@@ -175,10 +175,9 @@ spec:
         image: "{{ .Values.image }}:{{ .Values.imageTag }}"
         imagePullPolicy: "{{ .Values.imagePullPolicy }}"
         command:
-        - sh
+        - bash
         - -c
         - |
-          #!/usr/bin/env bash
           set -euo pipefail
 
           elasticsearch-keystore create
@@ -230,7 +229,7 @@ spec:
               - bash
               - -c
               - |
-                #!/usr/bin/env bash -e
+                set -e
                 # If the node is starting up wait for the cluster to be ready (request params: "{{ .Values.clusterHealthCheckParams }}" )
                 # Once it has started only check that the node itself is responding
                 START_FILE=/tmp/.es_start_file