tests: cmd: don't recurse

This confers an >10x speedup on t/z-t/cmd builds (12s -> 1.1s),
gets rid of 23 redundant identical automake specs and gitignores,
and groups the binaries with their common headers

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: John Kennedy <john.kennedy@delphix.com>
Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Closes #13259

tests/zfs-tests/cmd/send_doall.c

@@ -0,0 +1,87 @@
+/*
+ * CDDL HEADER START
+ *
+ * The contents of this file are subject to the terms of the
+ * Common Development and Distribution License (the "License").
+ * You may not use this file except in compliance with the License.
+ *
+ * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
+ * or http://www.opensolaris.org/os/licensing.
+ * See the License for the specific language governing permissions
+ * and limitations under the License.
+ *
+ * When distributing Covered Code, include this CDDL HEADER in each
+ * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
+ * If applicable, add the following below this CDDL HEADER, with the
+ * fields enclosed by brackets "[]" replaced with your own identifying
+ * information: Portions Copyright [yyyy] [name of copyright owner]
+ *
+ * CDDL HEADER END
+ */
+
+/*
+ * Portions Copyright 2020 iXsystems, Inc.
+ */
+
+/*
+ * Test a corner case : a "doall" send without children datasets.
+ */
+
+#include <libzfs.h>
+#include <libzfs_core.h>
+
+#include <fcntl.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <sysexits.h>
+#include <err.h>
+
+static void
+usage(const char *name)
+{
+	fprintf(stderr, "usage: %s snap\n", name);
+	exit(EX_USAGE);
+}
+
+int
+main(int argc, char const * const argv[])
+{
+	sendflags_t flags = { 0 };
+	libzfs_handle_t *zhdl;
+	zfs_handle_t *zhp;
+	const char *tofull, *fsname, *tosnap, *p;
+	int error;
+
+	if (argc != 2)
+		usage(argv[0]);
+
+	tofull = argv[1];
+
+	p = strchr(tofull, '@');
+	if (p == NULL)
+		usage(argv[0]);
+	tosnap = p + 1;
+
+	fsname = strndup(tofull, p - tofull);
+
+	zhdl = libzfs_init();
+	if (zhdl == NULL)
+		errx(EX_OSERR, "libzfs_init(): %s", libzfs_error_init(errno));
+
+	zhp = zfs_open(zhdl, fsname, ZFS_TYPE_FILESYSTEM);
+	if (zhp == NULL)
+		err(EX_OSERR, "zfs_open(\"%s\")", fsname);
+
+	flags.doall = B_TRUE;
+
+	error = zfs_send(zhp, NULL, tosnap, &flags,
+	    STDOUT_FILENO, NULL, NULL, NULL);
+
+	zfs_close(zhp);
+
+	libzfs_fini(zhdl);
+	free((void *)fsname);
+
+	return (error);
+}