Code findings after PR 386

[dirkjanfaber]

The review process of PR #386 found a couple of issues that need resolving (and postponed for this issue as the findings where already in the code before migrating).

All can be found in the src/nodes/victron-virtual/index.js file:

• Why stringify() and then parse(). Line 145 (Refactor/virtual device types #386 (comment))
• Dubious usage of actualDev vs dev: We use actualDev in the next line, but further down we use dev. Lines 108 (Refactor/virtual device types #386 (comment)) and 131 (Refactor/virtual device types #386 (comment))
• This object definition duplicates the object we return within the previous if(). I suggest to refactor this, so that the for (const key in ...) below iterates zero times if there are no properties. The return value at the end of the function will be the same (as the object returned in the previous if()). Around line 139 (Refactor/virtual device types #386 (comment))

And add extra test to increase code coverage:

• Refactor/virtual device types #386 (comment)