Add test to rename into root directory

The ancestor tests in rename were preventing renaming into the root
directory.

Signed-off-by: Zach Brown <zab@versity.com>

tests/golden/basic-posix-consistency

@@ -49,6 +49,7 @@ four
 --- can't overwrite non-empty dir
 mv: cannot move ‘/mnt/test/test/basic-posix-consistency/dir/c/clobber’ to ‘/mnt/test/test/basic-posix-consistency/dir/a/dir’: Directory not empty
 --- can overwrite empty dir
+--- can rename into root
 == path resoluion
 == inode indexes match after syncing existing
 == inode indexes match after copying and syncing

tests/tests/basic-posix-consistency.sh

@@ -149,6 +149,10 @@ find "$T_D0/dir" -ls 2>&1 | t_filter_fs > "$T_TMP.0"
 find "$T_D1/dir" -ls 2>&1 | t_filter_fs > "$T_TMP.1"
 diff -u "$T_TMP.0" "$T_TMP.1"
 rm -rf "$T_D0/dir"
+echo "--- can rename into root"
+touch "$T_D0/rename-into-root"
+mv "$T_D0/rename-into-root" "$T_M0/"
+rm -f "$T_M0/rename-into-root"
 
 echo "== path resoluion"
 touch "$T_D0/file"