Hard code the MAC key for remote provisioning

We need to be sure that MACs are valid across multiple reboots, so the
MAC key cannot change every time we start up the remote provisioning
context. For a temporary fix, hard-code the key so it's predictable.

Bug: 195292068
Test: RemoteProvisionerUnitTests
Change-Id: Ia98cc577ddceacbe0c9f84684137b515a7cfea42
1 file changed