Fix issue with incorrect model on MySQL

In 'Status' model, 'text' attribute is declared as String. SQLAlchemy
translates String type to VARCHAR type in MySQL dialect. When column
with VARCHAR type is declared in MySQL, user must specify
size of the column.

We can't specify size for text attribute because Reporter class from
core library that gives ability to publish different deployment statuses
from MuranoPL doesn't limit user input. Solution is to change attribute
type to Text.

Change-Id: If72e6db4b3c2039504f77649118ac9e1f68b8289
Closes-bug: #1341132
Merge "Fix issue with incorrect model on MySQL"