xfstests: make install support common/ and tests/ dirs

xfstests have some change on the organization of the testcases
and common* files:
     * The common* scripts have been reorganized into the common/ dir.
     * The testcases have been reorganized into sub test dirs under tests/.
     * The run.* scripts have been removed.

This patch uses the simple way to make install support above changes:
     Make up one Makefile for each newly created subdirs, which can control
     'make install' separately.

v2 introduces the following changes compared with v1:
     * Ignore the file 'group' under the top dir, for it's useless in the new
       structures.
     * Remove the redundant comments in the Makefiles.
     * Use XXX_DIR instead of XXX_SUBDIR in the Makefiles under common/ and tests/.
     * Export TESTS_DIR in teh top level Makefile instead of tests/Makefile.
     * Obtain the names of dirs for testcases by iterating sub dirs under /tests,
       not by enumeration in tests/Makefile.

Signed-off-by: Wang Sheng-Hui <shhuiw@gmail.com>
Reviewed-by: Rich Johnston <rjohnston@sgi.com>
[rjohnston@sgi.com Minor modification to Makefile]
Signed-off-by: Rich Johnston <rjohnston@sgi.com>

tests/Makefile

@@ -0,0 +1,19 @@
+#
+# Copyright (c) 2003-2005 Silicon Graphics, Inc.  All Rights Reserved.
+#
+
+TOPDIR = ..
+include $(TOPDIR)/include/builddefs
+
+TESTS_SUBDIRS = $(shell find . -maxdepth 1 -type d | sed -n -e 's/\.\///gp')
+
+include $(BUILDRULES)
+
+install: $(addsuffix -install,$(TESTS_SUBDIRS))
+	$(INSTALL) -m 755 -d $(PKG_LIB_DIR)/$(TESTS_DIR)
+
+# Nothing.
+install-dev install-lib:
+
+%-install:
+	$(MAKE) $(MAKEOPTS) -C $* install