Description of problem:

I'm using dnf inside a test script to resolve dependencies and download RPMs locally. The following command works fine:

# dnf install --releasever=26 --downloadonly --downloaddir=/tmp/dnf.download.2 --installroot=/tmp/dnf.root.2 java-1.8.0-openjdk-1.8.0.*


however it requires root privileges and we want to run as non-root. So I tried:

$ dnf download -v --releasever=26 --resolve --best --forcearch x86_64 --downloaddir=/tmp/dnf.download.1 --installroot=/tmp/dnf.install.1 java-1.8.0-openjdk-1.8.0.* 

This fails with:

Error in resolve


After adding some debugging into to download.py
```
            for msg in goal.problems:
                logger.debug(msg)
```

I got:


package java-1.8.0-openjdk-1:1.8.0.131-7.b12.fc26.i686 requires java-1.8.0-openjdk-headless(x86-32) = 1:1.8.0.131-7.b12.fc26, but none of the providers can be installed


Version-Release number of selected component (if applicable):

python3-dnf-plugins-core-2.1.5-4.fc27.noarch
dnf-2.7.5-2.fc27.noarch

How reproducible:
Always


Additional info:


Looking at the code inside download.py I get the feeling that the underlying hawkey.Goal object is not setup properly. In any case there is a self._goal object created in dnf's base.py so maybe use that.