improve building of rpm and deb packages.

[Rohja]

add systemd configuration.
set pm2's home to /etc/pm2.
create user/group on installation - clean after remove
add automatic setup script for debian-like and rhel-like distro.

To install on debian-like systems using a one-liner:
curl -sL https://raw.githubusercontent.com/Rohja/pm2/drone_build/packager/setup.deb.sh | sudo -E bash -

To install on rhel-like systems using a one-liner:
curl -sL https://raw.githubusercontent.com/Rohja/pm2/drone_build/packager/setup.rpm.sh | sudo -E bash -

@Unitech

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