Add support for mandatory remote configs in DynamicConfig feature

Also patch issue in which config with no key-value(s) pairs throws
JSONException on parsing.

bug: 77447857
Test: run gts-dev -m GtsOsTestCases
Change-Id: I213a60d1c39bd20e0e73d6a2e7016d9c5656d12f
3 files changed
tree: 707a95efe845e8da1b90c8f949c51c8eb441f44a
  1. common/
  2. tools/
  3. Android.mk
  4. test_defs.sh