Fixes to prepare-base.sh for the merged wifi setup

[dhylands]

This should fix #1241

[codecov-io]

Codecov Report

Merging #1242 into master will increase coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1242      +/-   ##
==========================================
+ Coverage   75.33%   75.35%   +0.01%     
==========================================
  Files         123      123              
  Lines        5916     5916              
  Branches      824      824              
==========================================
+ Hits         4457     4458       +1     
+ Misses       1287     1286       -1     
  Partials      172      172

Impacted Files	Coverage Δ
src/controllers/things_controller.js	79.82% <0%> (+0.42%)	⬆️

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[hobinjk]

LGTM with the existing config files in image/config removed. The inclusion of the systemd service file is also unnecessary. I don't understand why everything needs to be copied into the home directory for it to work but as long as it does work I'm okay with it

[dhylands]

The make-prep.sh script copies a few files (prepare-base.sh and prepare-base-root.sh) to the home directory. Most of the files the scripts needs are actually embedded inside the script itself as a "here" document.

At this stage, we're setting up to build the base image, so the gateway repository hasn't been checked out or anything.

I'd probably update the scripts to use "here" documents in the future. See this for an example:
https://github.com/mozilla-iot/gateway/blob/6724d401cee3ca278b5f448c9d5adcfccd1910b3/image/prepare-base.sh#L79-L101