stbt camera calibrate: Refactor: Inject device path
stbt camera calibrate: Refactor: Inject device path

Rather than reading it from `get_config` in sub-functions.  This makes the
code more functional and easier to read and reuse.  Specifically I wanted
to be able to reuse this from iPython notebooks.

martynjarvis/stb-tester,martynjarvis/stb-tester,martynjarvis/stb-tester,martynjarvis/stb-tester,LewisHaley/stb-tester,LewisHaley/stb-tester,stb-tester/stb-tester,martynjarvis/stb-tester,LewisHaley/stb-tester,LewisHaley/stb-tester,LewisHaley/stb-tester,stb-tester/stb-tester,LewisHaley/stb-tester,stb-tester/stb-tester,martynjarvis/stb-tester,stb-tester/stb-tester,LewisHaley/stb-tester,martynjarvis/stb-tester