Implement default handler for multiple client pre_execute
Implement default handler for multiple client pre_execute

Author: Tory Haavik <tory.haavik@twosigma.com>

Closes #1727 from toryhaavik/multiple and squashes the following commits:

557e854 [Tory Haavik] Implement default handler for multiple client pre_execute

ibis-project/ibis,cpcloud/ibis,cpcloud/ibis,cloudera/ibis,cloudera/ibis,cpcloud/ibis,cloudera/ibis,ibis-project/ibis,cpcloud/ibis,ibis-project/ibis,ibis-project/ibis