Use vector to pass around keys

In the future the key size for new master keys will increase.
To maintain backwards compatibility the size of the key
can no longer be assumed. To help communicate the actual
size of the key, it will be passed around in a vector.

Bug: 121272336
Test: Ran Keystore CTS tests against Walleye,
      no new test failures observed
Change-Id: Ie74eaf5226398e2300eb266ddda269473593e9d4
Merged-In: I4c05acb15b77959f2bf89abbdc325904fffb497a