Fix values merge in helm-operator

[obiesmans]

Fix values merge in helm-operator.

Values merges in helm-operator will overwrite instead of merge a dict that has it's keys
defined in more than two sources (e.g : Values and multiple ValuesFrom).

This happens because when merging,

flux/integrations/helm/release/release.go

Lines 507 to 514 in 6077df2

	destMap, isMap := dest[k].(map[string]interface{})
	// If the source map has a map for this key, prefer it
	if !isMap {
	dest[k] = v
	continue
	}
	// If we got to this point, it is a map in both, so merge them
	dest[k] = mergeValues(destMap, nextMap)

first iteration makes dest[k] a chartutil.Values and then at the next iteration will see isMap evaluate to False, overwriting instead of merging the two maps.

type Values map[string]interface{}

func main() {
    var v Values
    _, ok := interface{}(v).(map[string]interface{})
    fmt.Print(ok) // ok is false
}

I wrote a unit test that feed Values from a HelmRelease, a Configmap and a
Secret to make sure it fails, then changed mergValues signature to make it pass.

go test -v ./integrations/helm/release/
=== RUN   TestValues
--- FAIL: TestValues (0.00s)
    release_test.go:75:
        	Error Trace:	release_test.go:75
        	Error:      	Expected value not to be nil.
        	Test:       	TestValues
    release_test.go:76:
        	Error Trace:	release_test.go:76
        	Error:      	Expected value not to be nil.
        	Test:       	TestValues
FAIL
FAIL	github.com/weaveworks/flux/integrations/helm/release	0.498s

After the signature change :

go test -v ./integrations/helm/release/
=== RUN   TestValues
--- PASS: TestValues (0.00s)
PASS
ok  	github.com/weaveworks/flux/integrations/helm/release	0.242s

Fixes #1696.

[hiddeco]

This PR fixes #1696.

[stefanprodan]

LGTM

Thanks @obiesmans

[hiddeco]

Also looks good to me, thanks for getting to the bottom of this @obiesmans. 🌷