Use `set -e` in lpdev

When commands fail to execute, it can be easy to miss (eg, during a contract deploy procedure) and problems become more difficult to diagnose and trace later on. Use `set -e` to halt the execution of the lpdev script as soon as a command fails.

Will likely require some work to get everything flowing cleanly under various conditions.

Locate the lpdev script and first exercise the contract deploy procedure described in the issue, noting commands that can fail silently. Add failure halting while keeping expected conditions flowing cleanly, then verify that execution stops when a command fails.

Written by the indexing model from the issue text.