When you provision the space for the server in virt-manager or similar, you can set the disk space.
Then in the Fedora install you can select whole disk from the storage manager section.
Here is a similar issue by the same OP just recently.
AFAIK the user cannot, by default during installation, tell the OS to use the full drive as a single file system. The OS is limited in size when using fedora server and although it does use the entire drive space, it leaves the remainder of the drive beyond the minimal server OS space as an LVM space for use as the user sees fit.
@eliassal
If you wish to have the entire drive space already part of dedicated file systems the use of fedora server is not the best choice. If you are setting it up as a server then the default config is what you have already seen. It keeps the OS totally separate from the data space.
I note that for f43 there are 3 different images for download. One is a qcow2 image for a VM. The others are the normal live install iso and a netinstall iso.
Which image are you using to do your installation.?