This helps to get things consistent on Windows and Linux. Otherwise a path
like `/some/path` is absolute on one platform but not on the other. This is
mostly for getting the unit tests in this package to work on Windows, but
using absolute paths also helps in clarity of error logging.
Flamenco Manager now has a "storage path" config option, which will be
used by Shaman if enabled. Now the `{jobs}` implicit variable will always
exist, its value depending on whether Shaman is enabled or not.