enhancement: ignore field support slice type

[howieyuen]

What type of PR is this?

/kind feature

What this PR does / why we need it:

Which issue(s) this PR fixes:

Fixes #241

Special notes for your reviewer:

Slice type passes tests, use recursive type assertion can do that.
kind can not be specified, because ResourceNode supports k8s and tf, Type field is used to differ them.

Does this PR introduce a user-facing change?

enhancement: ignore field support slice type

Additional documentation e.g., design docs, usage docs, etc.:

None

[coveralls]

Pull Request Test Coverage Report for Build 4159591163

• 18 of 20 (90.0%) changed or added relevant lines in 1 file are covered.
• 31 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+0.08%) to 71.967%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
pkg/engine/operation/graph/resource_node.go	18	20	90.0%

Files with Coverage Reduction	New Missed Lines	%
pkg/engine/operation/graph/resource_node.go	31	60.5%

Totals
Change from base Build 4144172590:	0.08%
Covered Lines:	4644
Relevant Lines:	6453

---

💛 - Coveralls

[healthjyk]

1, add the option to specify the "type" may be better, more flexible;
2, if removeNestedField failed, why no error returned?
3, removeNestedField cannot handle nested field with type which is not map[string]interface{} or []interface{}, it's better to give clear indication of this func is only used for obj generated by json unmarshal, and show the process of json marshal and unmarshal in the test case.

[howieyuen]

1, add the option to specify the "type" may be better, more flexible; 2, if removeNestedField failed, why no error returned? 3, removeNestedField cannot handle nested field with type which is not map[string]interface{} or []interface{}, it's better to give clear indication of this func is only used for obj generated by json unmarshal, and show the process of json marshal and unmarshal in the test case.

1. the reason I wrote in the issue comment
2. remove nested field is inspired from k8s.io/apimachinery(pkg/apis/meta/v1/unstructured/helpers.go), it's a helper function, the only error, not such field, should not abort the apply process.
3. it's not for json marshall/unmarshall, generated manifests contain the user intent, this func is only use for ignored fields during preview step.

[healthjyk]

I saw the issue already, included the "type" is more useful for me.

[howieyuen]

I saw the issue already, included the "type" is more useful for me.

I'll try it again, see is there any better idea to make it.