The same thing happened to me on trusty, amd64 with the latest version of virtualbox 4.3.18. The strange thing is, dkms.conf was located in /var/lib/dkms/vboxhost/4.3.18/build/, but locate couldn't find it. It found the previous one, v4.3.16, but not the latest one. Only with "find" could I locate it.
The same thing happened to me on trusty, amd64 with the latest version of virtualbox 4.3.18. The strange thing is, dkms.conf was located in /var/lib/ dkms/vboxhost/ 4.3.18/ build/, but locate couldn't find it. It found the previous one, v4.3.16, but not the latest one. Only with "find" could I locate it.