Fix tablespace path TAP test of pg_verify_checksums for msys

TAP tests on msys need to run with the DTK perl, which understands msys
virtualized paths.  Postgres, however, does not understand such paths,
so before a path can be used safely with CREATE TABLESPACE, it needs to
be translated into a path on the underlying file system.

Per report from buildfarm member jacana.  Suggested fix is from Andrew
Dunstan.

Discussion: https://postgr.es/m/20181130053555.GF2267@paquier.xyz

src/bin/pg_verify_checksums/t/002_actions.pl

@@ -116,6 +116,7 @@ check_relation_corruption($node, 'corrupt1', 'pg_default');
 my $basedir = $node->basedir;
 my $tablespace_dir = "$basedir/ts_corrupt_dir";
 mkdir ($tablespace_dir);
+$tablespace_dir = TestLib::real_dir($tablespace_dir);
 $node->safe_psql('postgres',
 	"CREATE TABLESPACE ts_corrupt LOCATION '$tablespace_dir';");
 check_relation_corruption($node, 'corrupt2', 'ts_corrupt');