This allows more flexible control over the working directory. Values for workingDir must always start
with a / and will then be relative to the repo root.
The upside is that postgrest-with-postgresql-xxx postgrest-test-io works as expected
now. The downside is, that postgrest-with-postgresql-xxx psql now starts without
any schema. This now needs an explicit postgrest-with-postgresql-xxx -f path/to.sql
to do anything useful.
Resolves#2864
