build: fix install target using sudo

If you install with:

	sudo make install

Depending on the system, you may see that /var/lib/xfstests/
installed properly but /var/lib/xfstests/tests/ is empty and so your
install really is broken and not functional. Finding out what went
wrong is not obvious.

The issue is caused due to the fact that $(PWD) is used nad if sudo
is used this can be empty on some systems.

PWD is only used on one target on the xfstests build system, the
tests/*/ dir install target.

We can fix this by using $(CURDIR) instead.

This issue is observed on both Fedora and OpenSUSE, but not on
Debian.

Signed-off-by: Luis R. Rodriguez <mcgrof@kernel.org>
Suggested-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Eryu Guan <guaneryu@gmail.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>

tests/Makefile

@@ -5,7 +5,7 @@
 TOPDIR = ..
 include $(TOPDIR)/include/builddefs
 
-TESTS_SUBDIRS = $(sort $(dir $(wildcard $(PWD)/$(TESTS_DIR)/[a-z]*/)))
+TESTS_SUBDIRS = $(sort $(dir $(wildcard $(CURDIR)/[a-z]*/)))
 
 include $(BUILDRULES)