Change some LOG(DEBUG) to VLOG(plugin)

These log messages are somewhat spamy and we can collect them with
some related ones under VLOG(plugin).

Test: ./test.py --host
Test: ./test/run-test --host --dev --runtime-option -verbose:plugin 975
Change-Id: Ifae4be7891ccd09485b4c0edf98260739cace2f2
1 file changed