fix: logs error shadowing exec error

[rhbuf]

What

Rename an inner error to logsError to stop it shadowing the value of a higher scoped err.

Why

The assignment from io.ReadAll was overwriting the value of the original error and stopping the logs of the failed exec from being printed.

Implications

fixes #1171

Now when k3d image import fails the logs from the failed command will be logged (this is intended behaviour):

$ ../k3d/bin/k3d image import -c local -m direct test.tar
INFO[0000] Importing image(s) into cluster 'local'      
INFO[0000] Importing images from 1 tarball(s)...        
INFO[0000] Importing images '[test.tar]' into node 'k3d-local-server-0'... 
ERRO[0001] Failed to import image(s) into cluster 'local': could not load image to cluster from stream test.tar: error loading image to cluster, first error: failed to import images in node 'k3d-local-server-0': Exec process in node 'k3d-local-server-0' failed with exit code '1': Logs from failed access process:
ctr: unrecognized image format 
WARN[0001] At least one error occured while trying to import the image(s) into the selected cluster(s)

[iwilltry42]

Makes total sense, thank you!