It has been mentioned here: Debian8 (Jessie) on Turris Omnia and here: How to install nextcloud on a turris omnia debian jessie container (using apache2), there is a bug in the ISC DHCP client.
I tried this method and it seems to be working now, OpenMediaVault is being installed:
Another option might be this one:
Unfortunately, I got errors at the end of the installation:
Errors were encountered while processing:
nfs-common
nfs-kernel-server
openmediavault
E: Sub-process /usr/bin/dpkg returned an error code (1)
Any thoughts?