Report incompatible roles in pg_upgrade checking

Report incompatible roles in pg_upgrade checking

When checking for roles with a pg_ prefix in <= 9.5 servers, report
all found roles in a text file as how other checks are done instead
of just reporting that they exist. Rolenames are printed with their
Oids to match other reports.

Author: Daniel Gustafsson <daniel@yesql.se>
Reviewed-by: Bruce Momjian <bruce@momjian.us>
Reviewed-by: Michael Paquier <michael@paquier.xyz>
Discussion: https://postgr.es/m/4BB2735C-C347-4CF7-AFB1-8573BE930066@yesql.se