…h new SVG tree (#44)"

This reverts commit 3d31fd1.

The patch is for core master (v9) only and must not be part of
1.2.x tags / 8 branch.

The method must return an array. Properly mock that in
ViewHelperBaseTestcase.

After installation tests start from a clean slate, each test
must take care of cleaning up all leftovers from former test runs.

Before switching to a new frame, make sure
the performed action has been finished. In
Backend, the nprogress bar status can be used
for that.

Almost all Cests include the fully loaded routine
right after the useExistingSession call. In order
to ease the setup for new Cests, include the routine
into useExistingSession

master branch received lots of changes regarding acceptance testing,
while the v8 branch remained untouched. The patch ports the changes
back to 8 branch in order to activate ac tests in core v8 again.

…ser deprecation

FunctionalTestCase property $pathsToProvideInTestInstance handles
creation of target parent directory if it does not exist and can
copy directory structures recursive.

Closes: #107

If the instance to test is a composer-based installation, the vendor
folder is usually not situated in the docroot, but one level above.

Add a second check for this case.