clean up missing whitespace after ':'

Change-Id: I85a0348b978d4045ebb12a99f1bd9d5888a65b3b
Fix typo/bug in generic UC dropper

Change *fields -> *columns.

There should be tests for other backends mysql and postgres
but at this moment it is not so easy to implement it.

Fixes bug 1123848

Change-Id: I65a618760d499501589d5536c9f7dc64483b19ed
Add generic dropper for duplicate rows

Add generic function that help us to drop duplicated rows from table,
before creating unique constarints. It is very usefull in migrations,
because it will allow DBA to make migrations without IntegrityError
exceptions.

It deletes all duplicates of rows except row with max value in id column.

blueprint db-unique-keys

Change-Id: I7e48d3eb78cf9a5d30752541b143b0c9fa1f838a
Remove race condition (in TaskLog)

Delete all duplicate rows with same (task_name, host, period_beginning,
period_ending) expect one with the biggest value in `id` column.

Create UC on fields (task_name, host, period_beginning, period_ending)

Replace Select then Insert -> Try to Insert.

blueprint db-unique-keys

Change-Id: I99f45a6de6630482e9c56738f894cc55a37fffaf
Merge "clean up missing whitespace after ':'"
Merge "Fix typo/bug in generic UC dropper"
Merge "Add generic dropper for duplicate rows"
Merge "Remove race condition (in TaskLog)"