In key read tests, add usage flags that are suitable for the key type and
algorithm. This way, the call to exercise_key() in the test not only checks
that exporting the key is possible, but also that operations on the key are
possible.
This triggers a number of failures in edge cases where the generator
generates combinations that are not valid, which will be fixed in subsequent
commits.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
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