Add feature check for 'zpool resilver' command

The 'zpool resilver' command requires that the resilver_defer
feature is active on the pool. Unfortunately, the check for
this was left out of the original patch. This commit simply
corrects this so that the command properly returns an error
in this case.

Reviewed by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Igor Kozhukhov <igor@dilos.org>
Signed-off-by: Tom Caputi <tcaputi@datto.com>
Closes #8700

tests/zfs-tests/tests/functional/cli_root/zpool_resilver/zpool_resilver_bad_args.ksh

@@ -35,6 +35,8 @@
 # 1. Create an array containing bad 'zpool reilver' parameters.
 # 2. For each element, execute the sub-command.
 # 3. Verify it returns an error.
+# 4. Confirm the sub-command returns an error if the resilver_defer
+#    feature isn't active.
 #
 
 verify_runnable "global"
@@ -45,6 +47,13 @@ set -A args "" "-?" "blah blah" "-%" "--?" "-*" "-=" \
     "-A" "-B" "-C" "-D" "-E" "-F" "-G" "-H" "-I" "-J" "-K" "-L" \
     "-M" "-N" "-O" "-P" "-Q" "-R" "-S" "-T" "-U" "-V" "-W" "-X" "-W" "-Z"
 
+function cleanup
+{
+	log_must destroy_pool $TESTPOOL2
+	log_must rm -f $TEST_BASE_DIR/zpool_resilver.dat
+}
+
+log_onexit cleanup
 
 log_assert "Execute 'zpool resilver' using invalid parameters."
 
@@ -55,4 +64,8 @@ while [[ $i -lt ${#args[*]} ]]; do
 	((i = i + 1))
 done
 
+log_must mkfile $MINVDEVSIZE $TEST_BASE_DIR/zpool_resilver.dat
+log_must zpool create -d $TESTPOOL2 $TEST_BASE_DIR/zpool_resilver.dat
+log_mustnot zpool resilver $TESTPOOL2
+
 log_pass "Badly formed 'zpool resilver' parameters fail as expected."