Before the change, the first subtest in raw format tests just
generated messages and checked that they are added successfully. This
is not really a raw format test, it is creating of environment
required for other subtests to run. The patch removes the first
subtest from raw and replaces it with bare add_message calls, similar
to how it is done in other tests.
TODO: we should check that test environment was created successfully.
Currently, many tests do add_message(), notmuch new and other calls
without checking the results. We should come up with a general
solution for this, i.e. if any command during test initialization
fails, all tests should be skipped with appropriate error message.