Add keymint assumptions for attest key tests

Keys with an "attest" purpose are only valid with keymint, but we were
previously only checking a keystore feature flag. Now check both the
keystore feature as well as for keymint.

Test: AttestKeyTest
Bug: 241324025
Bug: 238705451
Change-Id: I9497d45ac5804356fcb12d08a521472d899c7dc1
(cherry picked from commit 8107a505b9872245ca145c76eff85151d5a44862)
1 file changed