Move tablespace path re-creation from the makefiles to pg_regress

Moving this logic into pg_regress fixes a potential failure with
parallel tests when pg_upgrade and the main regression test suite both
trigger the makefile rule that cleaned up testtablespace/ under
src/test/regress.  Even if pg_upgrade was triggering this rule, it has
no need to do so as it uses a different tablespace path.  So if
pg_upgrade triggered the makefile rule for the tablespace setup while
the main regression test suite ran the tablespace cases, it would fail.

61be85a was a similar attempt at achieving that, but that broke cases
where the regression tests require to run under an Administrator
account, like with Appveyor.

Reported-by: Andres Freund, Kyotaro Horiguchi
Reviewed-by: Peter Eisentraut
Discussion: https://postgr.es/m/20201209012911.uk4d6nxcnkp7ehrx@alap3.anarazel.de

src/tools/msvc/vcregress.pl

@@ -585,7 +585,6 @@ sub upgradecheck
 	my $outputdir          = "$tmp_root/regress";
 	my @EXTRA_REGRESS_OPTS = ("--outputdir=$outputdir");
 	mkdir "$outputdir"                || die $!;
-	mkdir "$outputdir/testtablespace" || die $!;
 
 	my $logdir = "$topdir/src/bin/pg_upgrade/log";
 	rmtree($logdir);