Reduce unnecessary long wait times on failing signal spies

Summary:
Several signal spies, which were supposed to fail, were waiting for the
default 5 seconds, which is most often unnecessary long.

This patch sets a time limit of 500ms in suitable cases. Reduces for me
the total test time by 40%.

Test Plan:
Before (with fixed seat and selection tests):
98% tests passed, 1 tests failed out of 45

Total Test time (real) = 173.31 sec

The following tests FAILED:

19 - kwayland-testWindowmanagement (Failed)

After:
98% tests passed, 1 tests failed out of 45

Total Test time (real) = 102.12 sec

The following tests FAILED:

19 - kwayland-testWindowmanagement (Failed)

Reviewers: Plasma, davidedmundson

Reviewed By: Plasma, davidedmundson

Subscribers: kde-frameworks-devel

Tags: Frameworks

Differential Revision: https://phabricator.kde.org/D14184