powerlog: Don't hijack logger when import as module
powerlog: Don't hijack logger when import as module

BRANCH=master
BUG=b:112865585,b:123259683
TEST=No log spam when import as module from autotest

Change-Id: I7ced102bbb893bc1baa88c625b8c7279a1e32677
Signed-off-by: Puthikorn Voravootivat <6b0bf59b07ec88a47755d311f85101e4220afc86@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/1437515
Commit-Ready: ChromeOS CL Exonerator Bot <fa429e5907f00867f797423aea74327bb02c91b6@appspot.gserviceaccount.com>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec