Rename karaage.util to karaage.common

Change-Id: I776d66e812d44bad7decfe7b0f41c1bb4e40b1ec
Move karaage/common/usage.py

Move karaage/common/usage.py to karaage/cache/usage.py

Change-Id: I772edf2ccc3a15f13287ebedf3095cc10b773ea0