ns clean - sometimes doesn't on Android

[NathanaelA]

Environment

• CLI: 7.0.x

Describe the bug
If Gradle(?) is still running in the background (or perhaps some other task) the platforms directory can be left in a state where you are now broken.

To Reproduce
Probably do something to cause gradle to fail after gradle works (so a gradle process is running in the background...)

Expected behavior
Clean cleans the folder, or WARNS that the clean was un-successful

Idea for Solution
We need to see if any files are left in the folder after a clean command, if any are left report it failed.