Openvpn can start automatically at boot-time. To do this, openvpn expects one or more files in /etc/openvpn, where the name end in .conf
If they are there, the startup-script wil pass these configfiles to openvpn and openvpn starts using this configfile.
Reading in this configfile, openvpn needs to know where to find the private, certificate and ca-certificate. They will be somewhere on disk (sd-card in case of a Raspberry PI) so openvpn needs to know exactly where to find these files.
Therefore the configfiles needs to point to these files with there full path:
ca /etc/openvpn/certs/cacert.pem
key /etc/openvpn/vcerts/private.key
cert /etc/openvpn/certs/cert.pem
Also make sure openvpn is started automatically, as root check:
update-rc.d openvpn defaults
Please let me know.