Ensure character columns are treated as string types.

[brianhartsock]

Closes #1194

I was playing around with dbt archive and hit the following failure:

2018-12-18 21:44:14,545 (Thread-1): Postgres error: Value too long for character type
DETAIL:  
  -----------------------------------------------
  error:  Value too long for character type
  code:      8001
  context:   Value too long for type character(1)
  query:     2816593
  location:  funcs_string.hpp:286
  process:   query3_106_2816593 [pid=13606]
  -----------------------------------------------

Tracking this down with debug mode, the column redacted_uuid char(36), in the original table definition (Redshift) was getting recreated as "redacted_uuid" character, in the dbt archive table.

Researching this lead me to schema.py where character columns are not interpreted as string types, therefore no size character length information is used when generating the create table statement.

To note, the query to generate columns for dbt returns the following info from my redshift table:

|column_name|data_type|character_maximum_length|numeric_size|
|---------------|---------|--||
|redacted_uuiid|character|36||

I don't know the implications of this change on other databases or functionality but it seems functionally more accurate. Also, I'm fine for the resulting column to be character varying(size) as the character column is generated from an ETL tool so it's a pain to change, which would have been my first quick fix.

Happy to adjust or change based on feedback - just throwing this up since it seemed like a valuable quick fix.

[drewbanin]

Hey @brianhartsock! This PR looks great -- nice work on adding a test :)

I just kicked off the tests in Circle -- that will run these tests with different versions of Python on pg/redshift/snowflake/bq. I think this looks pretty good to me as-is, but would also like to loop in @beckjake to take a quick look. I think we'll want to merge this for stephen-girard, right Jake?

[beckjake]

This PR looks good to me!

And I agree this should go in for dev/stephen-girard. The default branch is still at dev/grace-kelly, so I assume that's why it's the base.

[drewbanin]

LGTM!

[drewbanin]

Merged! Thanks @brianhartsock :)