Fix crash on insert into a table with an expression index

Fix crash on insert into a table with an expression index

We failed to set up a snapshot before calling UserTableUpdateOpenIndexes
during process_remote_insert, leading to a crash if the executor called
into anything that expects a snapshot. Like evaluation of expressions
in indexes.

Per report and fix from Abdul Yadi
https://abdulyadi.wordpress.com/2015/12/29/bdr-0-9-3-and-index-on-expression-part-3-solved/