Issue #672: Run cloudflared service without root

[romeroyonatan]

Run the cloudflared service with cloudflared user

• Create user cloudflared if it does not exist in cloudflared service install
• Remove user cloudflared in cloudflared service uninstall
• Add User=cloudflared in /etc/systemd/system/cloudflared.service

Note: this only works for systemd.

I tested it in our environment and it worked :)

Closes #672