[NEXUS-5956] Ignore walking exceptions and just log a warning

The fact that we could not clean up some files should not stop us from getting yum metadata from remote

Signed-off-by: Alin Dreghiciu <adreghiciu@gmail.com>
[NEXUS-5956] Organize imports

Signed-off-by: Alin Dreghiciu <adreghiciu@gmail.com>