Updated make file for docker building to perform extra sanity tests

[trzecieu]

Reapply #526

This change:

• Adds extra sanity tests for Makefile, so that it will be easier to maintain the image
• Switches to make commands for CircleCI, and adds test step
• Adds small changes to RADME.md to better reflect how to build image locally

To be merged after: #530

[sbc100]

lgtm % testing in CI without a CIRCLE_TAG

[sbc100]

There is no CIRCLE_TAG set when for build-docker-image I think. Its designed to run on all commits just not just releases.

[trzecieu]

Indeed just found that on the portal, added some fix for that in following commit.

[trzecieu]

Looks like it works just fine. So basically now it will always build against the latest tagged version.

[trzecieu]

@sbc100 after some fighting with CircleCi I was able to reproduce an original reason why I've added entrypoint:

# compilation as non-root
docker run --rm -u `id -u`:`id -g` -v `pwd`:/src -w /src emscripten/emsdk:1.39.18 \
		bash -c "\
			mkdir -p .test \
			&& echo 'int main() { return 0; }' > .test/main.c \
			&& emcc -c .test/main.c -o .test/main\
		"
Traceback (most recent call last):
  File "/emsdk/upstream/emscripten/emcc.py", line 42, in <module>
    import emscripten
  File "/emsdk/upstream/emscripten/emscripten.py", line 24, in <module>
    from tools import building
  File "/emsdk/upstream/emscripten/tools/building.py", line 23, in <module>
    from . import shared
  File "/emsdk/upstream/emscripten/tools/shared.py", line 1801, in <module>
    check_vanilla()
  File "/emsdk/upstream/emscripten/tools/shared.py", line 698, in check_vanilla
    is_vanilla_file = temp_cache.get('is_vanilla.txt', get_vanilla_file)
  File "/emsdk/upstream/emscripten/tools/cache.py", line 108, in get
    self.acquire_cache_lock()
  File "/emsdk/upstream/emscripten/tools/cache.py", line 55, in acquire_cache_lock
    self.filelock.acquire(60)
  File "/emsdk/upstream/emscripten/tools/filelock.py", line 240, in acquire
    self._acquire()
  File "/emsdk/upstream/emscripten/tools/filelock.py", line 360, in _acquire
    fd = os.open(self._lock_file, open_mode)
PermissionError: [Errno 13] Permission denied: '/.emscripten_cache.lock'
make: *** [test] Error 1

This is result of non-standard user used in Circle Ci (that is not 1000:1000).

Should I revert entrypoint and add support for that?

[sbc100]

I think the fix is that the emscripten root needs to be writable due to the code in emscripten that checks if the emscripten root is writable.

I think adding this line should fix it:

&&  chmod 777 ${EMSDK}/upstream/emscripten \ 

We should probably update the emscripten code so that only the cache directory (and not the containing directory need to be writable).

[sbc100]

Why the . prefix here? Why not just test?

[trzecieu]

not a particular reason, just convention - I can change that.

[sbc100]

Did you mean to not include -u here?