Clear out all dialog resources before adding/validating.

[h-kataria]

Clear out all dialog resources to make sure there is no invalid resources left from previous invalid transaction.

https://bugzilla.redhat.com/show_bug.cgi?id=1448274

@lgalis @eclarizio please test/review.

[miq-bot]

Checked commit h-kataria@b66aa8d with ruby 2.2.6, rubocop 0.47.1, and haml-lint 0.20.0
2 files checked, 0 offenses detected
Everything looks fine. ⭐

[lgalis]

Looks good - verified in the UI

[h-kataria]

@chessbyte can you please merge

[eclarizio]

The only thing I'm concerned about here is the test. Doing a lot of instance_variable_sets feels a little dirty and that means maybe something needs to be broken out. It is also really long and has a lot of steps in a single it block. It feels more like an acceptance test than a unit test, and I think because of that, again points to some refactoring that could be done. I don't think it's 100% necessary to do it in this PR, but I think it's a good thing to keep in mind going forward.

[simaishi]

Fine backport details:

$ git log -1
commit b464832dc438d88df7697a0407d34df91b7699a4
Author: Oleg Barenboim <[email protected]>
Date:   Mon May 8 13:50:57 2017 -0400

    Merge pull request #1306 from h-kataria/dialog_editor_add_element_fix
    
    Clear out all dialog resources before adding/validating.
    (cherry picked from commit 91a9c32ecab7d4fc7faac12391b7ee9ebedaedbb)
    
    https://bugzilla.redhat.com/show_bug.cgi?id=1448943