Squashed 'external/devlib/' changes from 7f5e0f5b..3c28c280

3c28c280 utils/check_output: Ensure `output` and `error` are always initialised.
b9d50ec1 utils/check_output: Only attempt to decode output if present.
7780cfdd utils/android: Combine stdout and stderror by combining the strings in adb_shell()
7c79a040 utils/misc: Revert d4b0dedc
779b0cbc utils/ssh: Only try SSH keys if no password is supplied.
b6cab646 docs: Add `LinuxTarget` and `LocalLinuxTarget` to the documentation
ec0a5884 docs: Update to use `module` diretive

git-subtree-dir: external/devlib
git-subtree-split: 3c28c280dee540972c047caae55c29e478f6eeb2