Copy dnf.conf to target userspace and allow a custom one

This change allows working around the fact that source and target
`dnf.conf` files might be incompatible. For example some of the proxy
configuration between RHEL7 and RHEL8.

If it exists, the `/etc/leapp/files/dnf.conf` config file will be
copied to the target userspace. Target system compatible configuration
can be specified there. If it doesn't exist, the `/etc/dnf/dnf.conf`
from the source system will be copied instead.

NOTE: The configuration is not copied onto the target system,
only to the target userspace.

repos/system_upgrade/common/actors/dnfconfuserspacecopy/actor.py

@@ -0,0 +1,24 @@
+from leapp.actors import Actor
+from leapp.libraries.actor import copycustomdnfconf
+from leapp.models import TargetUserSpacePreupgradeTasks
+from leapp.tags import FactsPhaseTag, IPUWorkflowTag
+
+
+class DNFConfUserspaceCopy(Actor):
+    """
+    Copy dnf.conf to target userspace
+
+    Copies /etc/leapp/files/dnf.conf to target userspace. If it isn't available
+    /etc/dnf/dnf.conf is copied instead. This allows specifying a different
+    config for the target userspace, which might be required if the source
+    system configuration file isn't compatible with the target one. One such
+    example is incompatible proxy configuration between RHEL7 and RHEL8 DNF
+    versions.
+    """
+    name = "dnf_conf_userspace_copy"
+    consumes = ()
+    produces = (TargetUserSpacePreupgradeTasks,)
+    tags = (FactsPhaseTag, IPUWorkflowTag)
+
+    def process(self):
+        copycustomdnfconf.process()

repos/system_upgrade/common/actors/dnfconfuserspacecopy/libraries/dnfconfuserspacecopy.py

@@ -0,0 +1,19 @@
+import os
+
+from leapp.libraries.stdlib import api
+from leapp.models import CopyFile, TargetUserSpacePreupgradeTasks
+
+
+def process():
+    src = "/etc/dnf/dnf.conf"
+    if os.path.exists("/etc/leapp/files/dnf.conf"):
+        src = "/etc/leapp/files/dnf.conf"
+
+    api.current_logger().debug(
+        "Copying dnf.conf at {} to the target userspace".format(src)
+    )
+    api.produce(
+        TargetUserSpacePreupgradeTasks(
+            copy_files=[CopyFile(src=src, dst="/etc/dnf/dnf.conf")]
+        )
+    )

repos/system_upgrade/common/actors/dnfconfuserspacecopy/tests/test_dnfconfuserspacecopy.py

@@ -0,0 +1,26 @@
+import os
+
+import pytest
+
+from leapp.libraries.actor import copycustomdnfconf
+from leapp.libraries.common.testutils import CurrentActorMocked, logger_mocked, produce_mocked
+
+
+@pytest.mark.parametrize(
+    "userspace_conf_exists,expected",
+    [(False, "/etc/dnf/dnf.conf"), (True, "/etc/leapp/files/dnf.conf")],
+)
+def test_copy_correct_dnf_conf(monkeypatch, userspace_conf_exists, expected):
+    monkeypatch.setattr(os.path, "exists", lambda _: userspace_conf_exists)
+
+    mocked_produce = produce_mocked()
+    monkeypatch.setattr(copycustomdnfconf.api, 'produce', mocked_produce)
+    monkeypatch.setattr(copycustomdnfconf.api, 'current_logger', logger_mocked())
+
+    copycustomdnfconf.process()
+
+    assert mocked_produce.called == 1
+    assert len(mocked_produce.model_instances) == 1
+    assert len(mocked_produce.model_instances[0].copy_files) == 1
+    assert mocked_produce.model_instances[0].copy_files[0].src == expected
+    assert mocked_produce.model_instances[0].copy_files[0].dst == "/etc/dnf/dnf.conf"