Fix #15651

Now that OC_SubAdmin is just a wrapper around OC\SubAdmin some unit
tests had to be fixed because they expected different behaviour.

Eventually they should move to properly mocked instances of OC\SubAdmin
of course

All IE versions are not able to properly upscale SVG icons unless the
said SVG files contain a "viewBox" attribute, which is not always the
case. Also we cannot guarantee that all third party apps will have this
attribute in their icons.

So for now, app icons will not be displayed in IE instead of broken
ones.