Makefile.am: Don't create "--" directory

Automake automatically appends "--" to @mkdir_p@. In case you have
a directory named "--" in your source tree, you can remove it using
the command "rm -rf -- --".

Reviewed-by: iustinp

Makefile.am

@@ -269,7 +269,7 @@ distcheck-hook:
 	fi
 
 install-exec-local:
-	@mkdir_p@ -- "$(DESTDIR)${localstatedir}/lib/ganeti" \
+	@mkdir_p@ "$(DESTDIR)${localstatedir}/lib/ganeti" \
 	  "$(DESTDIR)${localstatedir}/log/ganeti" \
 	  "$(DESTDIR)${localstatedir}/run/ganeti"