[Security] Replace exception mocks with actual exception instances.

It is done for two reasons:
* consistency - we use real exception objects in most of the code
* latest phpunit does not like the way we were creating mocks for exceptions (it could be also fixed by letting phpunit to call the original constructor)
minor #10621 [Security] Replace exception mocks with actual exception instances. (jakzal)

This PR was merged into the 2.3 branch.

Discussion
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[Security] Replace exception mocks with actual exception instances.

It is done for two reasons:
* consistency - we use real exception objects in most of the code
* latest phpunit does not like the way we were creating mocks for exceptions (it could be also fixed by letting phpunit to call the original constructor)

Commits
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9438f88 [Security] Replace exception mocks with actual exception instances.