shill: DBusServiceProxy: Reduce severity of missing service

Services may come up in slightly different orders at boot.
Therefore it's not strictly an error if a D-Bus name owner
is not present initially.  Reduce the severity of such
errors.  It's left a TODO to add a delayed error message.

BUG=chromium:498908
TEST="stop shill; stop modemmanager; start shill; grep ModemManager /var/log/messages"
TEST=No messages should appear, while one should appear in /var/log/net.log

Change-Id: I93d27907d77450ca843dc7a50478dff628e83282
Reviewed-on: https://chromium-review.googlesource.com/277272
Reviewed-by: mukesh agrawal <quiche@chromium.org>
Commit-Queue: Paul Stewart <pstew@chromium.org>
Tested-by: Paul Stewart <pstew@chromium.org>
1 file changed