LogPager/LogEventsList: Correct docs about $pattern parameter

LogPager/LogEventsList: Correct docs about $pattern parameter

$pattern is a boolean, it is documented as "Do a prefix search rather
than an exact title match". However, its type was incorrectly
documented to be a string, and the default value was '' instead of
false (which was harmless, as it is correctly treated as a boolean
value everywhere).

Change-Id: Id093d12891a231d5934f9908e619065afff7380e