cmdlib: Stop using proc.Log*

The Log* functions are re-exported through the LU. Inline use of string
formatting (“%”) was converted to additional arguments to Log* (unlike
“feedback_fn”, these functions support it). Some punctuation has been
removed from messages, as well as some small re-wordings.

Signed-off-by: Michael Hanselmann <hansmi@google.com>
Reviewed-by: Helga Velroyen <helgav@google.com>