tests: mocklib: prevent caching modules loaded by mocklib.require()

This is needed to ensure that subsequent wrapped require() calls (re)load
the mock modules instead of reusing the cached real module instances.

Signed-off-by: Jo-Philipp Wich <jo@mein.io>

tests/lib/mocklib.uc

@@ -179,6 +179,7 @@ global.mocklib = {
 
 		try {
 			res = require(module);
+			delete global.modules[module];
 		}
 		catch (e) {
 			ex = e;