Added default sdkconfig for qemu build for the mqtt publish example,
Added environment configuration for running the same test on target
or in qemu
Updated missing example tests per latest ttfw refactoring
loadable elf example is different for 2 reasons:
1. loadable elf binary don't have flasher_args.json, so we can't use normal
to get from CI artifacts
2. it don't have binary and don't need to downloaded binary to DUT. Some
related functions can be ignored
use CI dependencies could waste a lot bandwidth for target test jobs, as
example binary artifacts are very large. Now we will parse required
artifacts first, then use API to download required files in artifacts.
