Fix argument checking in LUSetClusterParams

This patch fixes two issues with LUSetClusterParams and argument
checking.

First, this LU used the wrong function name (CheckParameters instead of
CheckArguments), which means that no parameter checking was done at all;
this impacted the candidate_pool_size checks (the only one done at this
stage).

Second, int() can raise both ValueError and TypeError, and we should
correctly handle both.

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Guido Trotter <ultrotter@google.com>