FIX: it should upgrade to new version instead of the old one

[paologallinaharbur]

What this PR does / why we need it:
When testing the upgrade we should actually install the new version

Old behaviour (installing the same version, not catching the issue with selectors)

Testing upgrades of chart 'nri-prometheus => (version: "2.1.2", path: "charts/nri-prometheus")' relative to previous revision 'nri-prometheus => (version: "2.1.1", path: "ct_previous_revision2130172757/charts/nri-prometheus")'...
[...]
>>> helm install nri-prometheus-y2dumyevqw ct_previous_revision2130172757/charts/nri-prometheus --namespace ct --wait --values ct_previous_revision2130172757/charts/nri-prometheus/ci/test-lowdatamode-values.yaml
>>> helm upgrade nri-prometheus-y2dumyevqw ct_previous_revision2130172757/charts/nri-prometheus --namespace ct --reuse-values --wait

New Behaviour (installing the new version, catching the issue)

Testing upgrades of chart 'nri-prometheus => (version: "2.1.2", path: "charts/nri-prometheus")' relative to previous revision 'nri-prometheus => (version: "2.1.1", path: "ct_previous_revision78831704/charts/nri-prometheus")'...
[...]
>>> helm install nri-prometheus-avhvhn5q0a ct_previous_revision78831704/charts/nri-prometheus --namespace ct --wait --values ct_previous_revision78831704/charts/nri-prometheus/ci/test-lowdatamode-values.yaml
>>> helm upgrade nri-prometheus-avhvhn5q0a charts/nri-prometheus --namespace ct --reuse-values --wait
Error: UPGRADE FAILED: cannot patch "nri-prometheus" with kind Deployment: Deployment.apps "nri-prometheus" is invalid: spec.selector: Invalid value: v1.LabelSelector{MatchLabels:map[string]string{"app.kubernetes.io/name":"nri-prometheus"}, MatchExpressions:[]v1.LabelSelectorRequirement(nil)}: field is immutable

Which issue this PR fixes

Fix #433

Special notes for your reviewer:

Please let me know if I am misunderstanding the feature or the code (it is a vely likely possibility 😄 )

[paologallinaharbur]

If interested, it would make sense as well to add some tests to cover the bug (if that's a bug 😅 ). For example with two charts having as only difference the selectors, like:

		{
			"change immutable deployment.spec.selector field in new version of the chart,
			"test_charts/simple-deployment",
			"test_charts/simple-deployment-different-selector",
			processError,
		},

---

Moreover, it would make sense to garbage collect the upgrade test change immutable deployment.spec.selector field since it covers helm/charts#7726 that it is due to apps/v1beta1, but it using to do so a v1 chart, .

[paologallinaharbur]

Hello @cpanato, 😄
do you know who can we ask to in order to know if it is a bug of the --upgrade flag or not?
I had the feeling that at least in our use case it is a possible source of false positives

[LeoColomb]

I also believe it's a bug, and this fix seems relevant.
Should also close #198

[cpanato]

i guess this is correct