Work around missing nodejs bug

[jasonaowen]

We previously discovered a bug in nodesource, and reported it upstream: nodesource/distributions#1262 . They haven't fixed that bug yet, so in the meantime we need to work around it.

Test for the presence of /usr/bin/nodejs during image building, and if it is missing, create it with

update-alternatives --quiet --install /usr/bin/nodejs nodejs \
    /usr/bin/node 50 \
    --slave /usr/share/man/man1/nodejs.1.gz nodejs.1.gz \
    /usr/share/man/man1/node.1.gz

[xmunoz]

@jasonaowen which images need node? All of them? Just backend?

[jasonaowen]

@xmunoz yes, just backend, but I think our image building step is for all images in all environments, and the terraform steps are for each entire environment.