Add tests from the old svn tree

We're losing the svn history (which we could probably keep if we tried
hard enough) but don't consider that worthwhile.

Note these tests are destructive, so run them only in a throwaway
environment like a chroot, container, or vm.

The tests/run.all script should be the one which launches all the tests.

Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>

tests/common/unlink_failure.c

@@ -0,0 +1,51 @@
+/* 
+ * gcc unlink_failure.c -o unlink_failure.so -shared -ldl 
+ * LD_PRELOAD=./unlink_failure.so FAILURE_PATH=/etc/shadow ./test /etc/shadow
+ */
+
+#define _GNU_SOURCE
+#include <dlfcn.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <stdarg.h>
+#include <fcntl.h>
+#include <string.h>
+#include <errno.h>
+#include <assert.h>
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+
+typedef int (*unlink_type) (const char *path);
+static unlink_type next_unlink;
+
+static const char *failure_path = NULL;
+
+int unlink (const char *path)
+{
+	if (NULL == next_unlink)
+	{
+		next_unlink = dlsym (RTLD_NEXT, "unlink");
+		assert (NULL != next_unlink);
+	}
+	if (NULL == failure_path) {
+		failure_path = getenv ("FAILURE_PATH");
+		if (NULL == failure_path) {
+			fputs ("No FAILURE_PATH defined\n", stderr);
+		}
+	}
+
+	if (   (NULL != path)
+	    && (NULL != failure_path)
+	    && (strcmp (path, failure_path) == 0))
+	{
+		fprintf (stderr, "unlink FAILURE %s\n", path);
+		errno = EBUSY;
+		return -1;
+	}
+
+	return next_unlink (path);
+}
+