Improved election pallet testing (#12327)

* Improved election pallet testing

* fmt

* remove comment

* more checks

* fixes in logic

* roll_to_signed

* switch to roll_to_signed

* Update frame/election-provider-multi-phase/src/mock.rs

Co-authored-by: Kian Paimani <[email protected]>

* remove useless checks

* remove warning

* add checks to signed.rs

* add some checks to unsigned.rs

* fmt

* use roll_to_signed and roll_to_unsigned

* remove nonsense

* remove even more nonsense

* fix

* fix

* remove useless checks

Co-authored-by: Kian Paimani <[email protected]>
Co-authored-by: parity-processbot <>