doc: automake: Add support for sphinx 4.0.

File layout for man pages in sphinx 4 by default changed [1] from:

  Documentation/_ref/man/page.section

 to:

  Documentation/_ref/man/section/page.section

Ajusting our build scripts so they will be able to locate files
in new places.  This fixes our CI build.

[1] sphinx-doc/sphinx#7996

Signed-off-by: Ilya Maximets <i.maximets@ovn.org>
Acked-by: Ben Pfaff <blp@ovn.org>
Reviewed-by: David Marchand <david.marchand@redhat.com>
Reviewed-by: Aaron Conole <aconole@redhat.com>

Documentation/automake.mk

@@ -217,8 +217,13 @@ install-man-rst: docs-check
 	    $(extract_stem_and_section); \
 	    echo " $(MKDIR_P) '$(DESTDIR)'\"$$mandir\""; \
 	    $(MKDIR_P) '$(DESTDIR)'"$$mandir"; \
-	    echo " $(INSTALL_DATA) $(SPHINXBUILDDIR)/man/$$stem.$$section '$(DESTDIR)'\"$$mandir/$$stem.$$section\""; \
-	    $(INSTALL_DATA) $(SPHINXBUILDDIR)/man/$$stem.$$section '$(DESTDIR)'"$$mandir/$$stem.$$section"; \
+	    if test -f $(SPHINXBUILDDIR)/man/$$stem.$$section; then \
+	        filepath=$(SPHINXBUILDDIR)/man/$$stem.$$section; \
+	    else \
+	        filepath=$(SPHINXBUILDDIR)/man/$$section/$$stem.$$section; \
+	    fi; \
+	    echo " $(INSTALL_DATA) $$filepath '$(DESTDIR)'\"$$mandir/$$stem.$$section\""; \
+	    $(INSTALL_DATA) $$filepath '$(DESTDIR)'"$$mandir/$$stem.$$section"; \
 	done
 else
 install-man-rst: