Add newline char to avoid mix of logs
Add a '\n' after "unpacking xxx..." to avoid mix of logs such as:
```
unpacking sha256:a7776895af32e34b1fef997e26c79fa988b40c5cf2a3fb48dc22e0584b648d82...DEBU[0005]
Extraction not needed, layer snapshot exists
DEBU[0005] Extraction not needed, layer snapshot exists
DEBU[0005] Extraction not needed, layer snapshot exists
DEBU[0005] Extraction not needed, layer snapshot exists
DEBU[0005] Extraction not needed, layer snapshot exists
DEBU[0005] Extraction not needed, layer snapshot exists
done
```
After this commit:
```
unpacking sha256:a7776895af32e34b1fef997e26c79fa988b40c5cf2a3fb48dc22e0584b648d82...
DEBU[0008] Extraction not needed, layer snapshot exists
DEBU[0008] Extraction not needed, layer snapshot exists
DEBU[0008] Extraction not needed, layer snapshot exists
DEBU[0008] Extraction not needed, layer snapshot exists
DEBU[0008] Extraction not needed, layer snapshot exists
DEBU[0008] Extraction not needed, layer snapshot exists
done
```
Signed-off-by: Zhang Wei <zhangwei555@huawei.com>