0.12.0-alpha regression: on-run-start|end hooks can no longer be supplied as strings

[drewbanin]

Issue

Issue description

This worked in 0.11.x

# dbt_project.yml

on-run-start: "select 1 as id"
on-run-end: "select 2 as id"

whereas now it results in:

`Invalid arguments passed to "Project" instance: on-run-end.'select 1 as id' is not of type 'array'`

dbt should marshal the hook declarations into an array if a string is provided. This is the same behavior that's currently implemented for pre-hook and post-hook configs.

System information

The output of dbt --version:

0.12.0-a2

Steps to reproduce

# dbt_project.yml

on-run-start: "select 1 as id"
on-run-end: "select 2 as id"

$ dbt compile