t3008: skip lazy-init test on a single-core box

The lazy-init codepath will not be exercised uniless threaded.  Skip
the entire test on a single-core box.  Also replace a hard-coded
constant of 2000 (number of cache entries to manifacture for tests)
with a variable with a human readable name.

Signed-off-by: Kevin Willford <kewillf@microsoft.com>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Jeff Hostetler <jeffhost@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t3008-ls-files-lazy-init-name-hash.sh

@@ -4,14 +4,22 @@ test_description='Test the lazy init name hash with various folder structures'
 
 . ./test-lib.sh
 
+if test 1 -eq $($GIT_BUILD_DIR/t/helper/test-online-cpus)
+then
+	skip_all='skipping lazy-init tests, single cpu'
+	test_done
+fi
+
+LAZY_THREAD_COST=2000
+
 test_expect_success 'no buffer overflow in lazy_init_name_hash' '
 	(
-	    test_seq 2000 | sed "s/^/a_/"
+	    test_seq $LAZY_THREAD_COST | sed "s/^/a_/"
 	    echo b/b/b
-	    test_seq 2000 | sed "s/^/c_/"
+	    test_seq $LAZY_THREAD_COST | sed "s/^/c_/"
 	    test_seq 50 | sed "s/^/d_/" | tr "\n" "/"; echo d
 	) |
-	sed -e "s/^/100644 $EMPTY_BLOB	/" |
+	sed "s/^/100644 $EMPTY_BLOB	/" |
 	git update-index --index-info &&
 	test-lazy-init-name-hash -m
 '