Add build essential to tbe bionic stack build image

[kardolus]

Hi there,

currently the go-cnb does not work on the bionic stack.

It requires gcc to work. @sclevine mentioned that adding build essential to the bionic stack will resolve this.

[nebhale]

I'd discourage us actually including build-essential in the bionic stack. The ubuntu:bionic image is currently 64.2M and including build-essential adds 221M for a ~450% size increase. This should be handled as a mixin.

[sclevine]

Just to clarify: we’d only add this to the build image, not the run image. We may want to special-case build tools that don’t break linkages at runtimes.