tests: use local nanosleep based sleep utility replacement

* tests/sleep.c: New file.
* tests/.gitignore: Add sleep.
* tests/Makefile.am (check_PROGRAMS): Likewise.
* tests/count.test: Use it instead of system sleep utility.
diff --git a/tests/Makefile.am b/tests/Makefile.am
index 8a91871..6535030 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -130,6 +130,7 @@
 	signalfd \
 	sigreturn \
 	stack-fcall \
+	sleep \
 	stat \
 	stat64 \
 	statfs \