man: create parent directories in install recipe

Support the use of `make install` in packaging scripts, where the
$mandir tree might not exist under $DESTDIR.

For portability, create the parent directories using a separate install
command instead of relying on the non-portable `-D` flag.

Set errexit so the install target fails if any install step fails.

Signed-off-by: Cory Snider <csnider@mirantis.com>

man/Makefile

@@ -35,7 +35,9 @@ man%:
 
 .PHONY: install
 install: all
+	@set -ex; \
 	for sec in $(sections); do \
+		$(INSTALL) -d $(DESTDIR)$(mandir)/man$$sec && \
 		$(INSTALL_DATA) man$$sec/* $(DESTDIR)$(mandir)/man$$sec; \
 	done