Fix logging command in Linux/Cache multiwait

The logging command that tracks the options being sent to the multiwait is
incorrect in the Linux/Cache class.  All others cast the options list to a
string before writing to log.  Fix the Linux/Cache one so that the casting
is done.

OSEHRA-Id: http://issues.osehra.org/browse/OAT-111
Change-Id: I0061790a6b61cb5b2db71f5c9cbb8fdf6881a40f
Merge "Fix logging command in Linux/Cache multiwait"