Key generation should check for key id conflicts with newly created keys too

Job #1632735 failed for 0ebacc63:

I:kasp:check number of keys for zone ecdsa256.kasp in dir ns3 (203)
I:kasp:error: bad number of key files (2) for zone ecdsa256.kasp (expected 3)
I:kasp:check key id 26891
I:kasp:check key id 22631
I:kasp:KEY1 ID 22631
I:kasp:KEY2 ID no
I:kasp:error: No KEY2 found for zone ecdsa256.kasp
I:kasp:KEY3 ID 26891
I:kasp:failed

This test creates two new keys with the same key ID. The keymgr checks for conflicts, but only with already existing keys.