package/systemd-hacks: improve mongoose service file

and install a config file
package/*/*.mk: use "set -e" in for-loops

replace
   for x in ...; do cmd-a||cmd-b||exit; done;
with
   set -e; for x in...; do cmd-a||cmd-b; done;

for better-initramfs.mk, this is a cosmetic change (mostly),
systemd-hacks.mk had no "|| exit" in its for-loop before this commit.