Add JSON output to the RKP factory tool

The JSON format is suitable for uploading as test data. It also
includes the build fingerprint, which is required by the backend
to associate the CSR with a particular device family.

Ignore-AOSP-First: No automerge to aosp, will manually backport.
Bug: 191301285
Test: Manually run the tool with various --output_format flags
Change-Id: I1d787271c52a25df2d16a6d88dd7b278407ff4b7
1 file changed