[MRG] Update base image used for memory limit checks

[betatim]

Locally this still fails :-/

[betatim]

It seems like (locally) the limit doesn't actually get applied/used :-/ I'll need a bit of time to investigate what is going on.

[Xarthisius]

Locally this still fails :-/

@betatim I vaguely remember that I had problem imposing mem limits for docker using python API. It accepted the size notation but it wasn't setting the limit properly. I'd try to use number of bytes explicitly.

[betatim]

When we finally actually call the docker client the size is an integer without a postfix :-/

[betatim]

Mystery solved. The docker-py documentation says that a value of -1 will disable swap, which we were using. However https://docs.docker.com/engine/reference/commandline/build/ specifies that -1 means "unlimited swap". In the docker-py code I can't find anywhere where they do processing of the values we passed in.

Updated our code to reflect this new knowledge. Though I am confused why all tests have passed on travis (for 5adc4b2) when they fail locally. Speculation: there is no swap for the whole machine on travis?

[yuvipanda]

I dug around a bit more, and found docker/docs#4335. Is there a reason we're setting memory swap to be one byte more, instead of exactly the same?

[betatim]

When I had it set to 1 (a guess for "if we can't disable then let's use 1byte") I got an error the said "swap has to be bigger than memory limit", I didn't check if they actually meant "equal or larger". Checking now.

[betatim]

Looks like setting it to the same amount works! That is a nicer solution :D Thanks for asking.

[yuvipanda]

@betatim awesome! I changed the comment around it a little, otherwise it LGTM.

[yuvipanda]

Merged with @betatim's blessing. <3