Change alarm_history.detail to text type

The existing alarm_history.detail column size is 255 chars,
which is not enough for some large JSON payloads.

Change to Text column to make sure we store all detail.

Change-Id: I1b4ebee33954acc1f41a4cf0d0b991055b7d4fe9
Closes-Bug: #1236861
Signed-off-by: Stephen Gran <stephen.gran@guardian.co.uk>
Merge "Change alarm_history.detail to text type"