mongodb chart: respect existingSecret in standalone deployment

[xornet-sl]

Is this a request for help?:

---

Is this a BUG REPORT or FEATURE REQUEST? (choose one):
This is a BUG

Version of Helm and Kubernetes:
Helm version 2.9.1
Kubernetes version 1.11.0

Which chart:
stable/mongodb chart version 4.0.4

What happened:
standalone mongodb doesn't respect .Values.existingSecret but replicaset does.

What you expected to happen:
Secret handling with and without replicaset should be similar.

How to reproduce it (as minimally and precisely as possible):

helm install -n mongodb --set replicaSet.enabled=false --set usePassword=true --set existingSecret=mongodb --set fullnameOverride=mongodb stable/mongodb

This command will fail with Error: release mongodb failed: secrets "mongodb" already exists if there is a precreated secret with name mongodb.
Moreover helm delete --purge mongodb will delete this "existing", predefined secret.
if we omit --set fullnameOverride it will create another secret (i.e. won't use --set existingSecret).

Anything else we need to know:

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Any further update will cause the issue/pull request to no longer be considered stale. Thank you for your contributions.

[sfitts]

Just wanted to report the same issue. Has not been addressed so hopefully it won't get aged out (makes the chart hard to use unless you only enable the replica set).

Dup of #6340 I believe.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Any further update will cause the issue/pull request to no longer be considered stale. Thank you for your contributions.

[stale]

This issue is being automatically closed due to inactivity.