Add readme for the library and command line tool

Give a quick overview of `libhwtrust` and `hwtrust` in a readme. Add a
couple of basic tests for the `hwtrust` CLI behaviour described in the
readme. Tidy up the build rules and make all the tests unit tests which
don't need to be explicitly listed in TEST_MAPPING.

Fix: 264913964
Test: atest libhwtrust_tests hwtrust_tests hwtrust_cli_tests
Change-Id: I8284d4ab0789d93e7b4bccffaf1162e59b2a5e18
4 files changed
tree: c4ddc264f3a1f58ff972f48a54af5b5319e656c6
  1. fuzzing/
  2. gdb/
  3. remote_provisioning/
  4. sanitizer-status/
  5. CleanSpec.mk
  6. OWNERS
  7. PREUPLOAD.cfg