Those per se are not that annoying, but the random messages generated
by the backend while pg_arman is waiting for segments to be archived
are annoying. This commit gets rid of them by using client_min_messages
set to warning on the connection used.
Report by Yury Zhuravlev.
This new facility has the advantage on not relying on static data when
generating the tests making the whole facility more robust. This is
basically taken from the upstream project pg_rman and adapted for the
sake of this pet project, so most of the credit go to Kyotaro Horiguchi
and Amit Langote regarding this facility. However I have adapted a bunch
of things and fixed a lot of redundancy and code duplication.