Added various vts tests for attestKey.

  - Added tests for signing attest key with factory chain.
  - Added test for signing encryption keys.
  - Added tests for chaining many RSA attest keys on the same chain.
  - Added tests for chaining many Ec attest keys on the same chain.
  - Added tests for alternate chaining of rsa-ec-rsa-ec-rsa attesti
    keys on the same chain.

Test: atest VtsAidlKeyMintTargetTest
Change-Id: I9c67e2b928d6bba6cc4074a4b65f639f33c9ec26