* Work around GCC-9 warning treated as error
```
../source/opt/instruction.h:101:23: error: '*((void*)& operand +32)' may be used uninitialized in this function [-Werror=maybe-uninitialized]
101 | uint64_t result = uint64_t(words[0]);
```
* Migrate all Kokoro build scripts over to use the docker VM image
Required updating the NDK SDK and build scripts, as well as the check_copyright for handling 2021.
