test progress API: removed simplistic check_progress() idea

The check_progress() idea is too simplistic for what we aim for,
so let's remove it to prevent test writers from depending on it.

Also, rename communicate_state() to report_state().

Signed-off-by: Cleber Rosa <crosa@redhat.com>
Merge pull request #172 from clebergnu/report_state

test progress API: removed simplistic check_progress() idea