Errors due to bad client requests (e.g., NotFound, BadRequest)
are logged as exception/trace level and it is annoying
from the point of operators' view.
This commit changes the log level for errors due to
user requests (HTTP 4xx errors) to INFO.
Closes-Bug: #1282394
Change-Id: Ic5646333db88ce856f9366e914cf961890d30501