Add an executable to create a microdroid signature

This is for testing purpose. Creating a microdroid signature and
embedding it in a payload image will be done by VirtManager in the
future.

Bug: 185069443
Test: create a signature following README
      create a payload.img with signature
      pass --disk=payload.img (check manually /dev/block/vdc1)
Change-Id: I6504dc6b3732c8e00e3bd1ffa5059995962d14b8
6 files changed
tree: c0d9960e09d8a493c200128d7d60c9305ef5a902
  1. apex/
  2. authfs/
  3. docs/
  4. microdroid/
  5. tests/
  6. virtmanager/
  7. vm/
  8. .clang-format
  9. PREUPLOAD.cfg