Add option --deb-systemd-path

[skoef]

This option will allow you to override the path within the staging directory systemd service files are moved to in debian packages.

On some systems systemd should not go in the hardcoded /lib/systemd/system but in /usr/lib/systemd/system instead. Many systems have the both symlinked, but not all so assuming /lib/systemd/system can be dangerous.

[jordansissel]

Tested, works! Thank you for improving fpm :)

Test:

% touch /tmp/example.service ; bundle exec bin/fpm -s empty -t deb --deb-systemd-path fancypants --deb-systemd /tmp/example.service -n example
Adding action files
Created package {:path=>"example_1.0_all.deb"}

% ar p example_1.0_all.deb data.tar.gz | tar -zt | grep example.service
./fancypants/example.service

And testing default behavior:

% touch /tmp/example.service ; bundle exec bin/fpm -s empty -t deb --deb-systemd /tmp/example.service -n example
Adding action files
Created package {:path=>"example_1.0_all.deb"}

% ar p example_1.0_all.deb data.tar.gz | tar -zt | grep example.service
./lib/systemd/system/example.service

[Jmennius]

This also helps with installing user services under /usr/lib/systemd/user!