Downgrade the log level when automatic confirm_resize fails

When CONF.resize_confirm_window is not 0, the unconfirmed migration
will be confirmed automatically after CONF.resize_confirm_window
seconds; it might fail due to reason such as instance is locked etc,
so failed to automatically confirm resize is not unexpected.
Downgrade the log from error to debug and after all, user can
either confirm it later or next automatically confirm might success.
Also modify the format of log as well.

Change-Id: I525c803d5e149c49606bcd460e2abb4c9300454a
Scheduler: enable scheduler hint to pass the group name

Commit ea6d8403bdc3c1d3ede87a2ed1c8740420c32080 partially
dealt with the problem. The actual scheduling would fail when
the group name was passed.

Change-Id: I668621770e59504164af9a2e861a59e900300bba
Closes-bug: #1303360
Merge "Downgrade the log level when automatic confirm_resize fails"
Merge "Scheduler: enable scheduler hint to pass the group name"