Add .log file ending to tap test log files

[Andres Freund]

Hi,

Right now it's harder than necessary to capture the log output from tap
tests because the the regression tests files don't end with a common
file ending with other types of logs.  They're
        # Open the test log file, whose name depends on the test name.
        $test_logfile = basename($0);
        $test_logfile =~ s/\.[^.]+$//;
        $test_logfile = "$log_path/regress_log_$test_logfile";

This was essentially introduced in 1ea06203b82: "Improve logging of TAP tests."

Would anybody object to replacing _logfile with .log? I realize that'd
potentially would cause some short-term pain on the buildfarm, but I
think it'd improve things longer term.

Greetings,

Andres Freund