test-lessons.sh: Add a workshop collection repository

As an example of what Software Carpentry would provide as a workshop
template.  Running this version of the script ends with:

  .
  ├── README.md
  ├── bower.json
  └── bower_components
      ├── git-lesson
      │   ├── README.md
      │   └── bower.json
      └── shell-lesson
          ├── README.md
          └── bower.json

  3 directories, 6 files
  bower check-new     Checking for new versions of the project dependencies..
  swc-workshop /tmp/student-workshop
  └─┬ git-lesson#0.1.0
    └── shell-lesson#0.2.0
test-lessons.sh: Use tabs and spaces to indent here-documents

When you create a here-document with '<<-', leading tabs are stripped
[1].  Because I still want indentation in the bower.json files, I
guess I'll have to use spaces for the indentation I want to preserve.

[1]: http://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_07_04
test-lessons.sh: Slot in a custom, per-workshop shell lesson

Running this version of the script ends with:

  swc-workshop /tmp/student-workshop
  ├─┬ git-lesson#0.1.0
  │ └── shell-lesson#0.3.0 (0.2.0 available)
  └── shell-lesson#0.3.0