Make a bigger column for storing task results in mysql

This patch adds new 2 types called BigText that actually use LongText
instead of Text in case of mysql

And use this new type for colum with task results

Change-Id: I6878e07f9d22257f45aa3d92fcfe9f15f1eef897
Closes-bug: #1300181
Merge "Make a bigger column for storing task results in mysql"