Removed duplicate spawn code in PowerVM driver

After introducing resize/migrate in PowerVM there was
some code that was duplicated after a rebase. The commit
removes the duplicate code. The functionality of
resize/migrate remains the same as introducted in
Change I72345626

Bug #1130680

Change-Id: I1fe3d8e1f2a19fd40a03c8c38d90c01711356b38
Remove race condition (in Networks)

Soft delete all duplicate rows with the same vlan except one with
the biggest value in `id` column.

Create UC on fields (vlan, deleted)

Replace Select then Insert -> Try to Insert.

Fix error in network_update method. We were able to update
vlan to duplicate.

Fix typo in description of method drop_old_duplicate_entries_from_table()

blueprint db-enforce-unique-keys

Change-Id: Ia1b58ab5a5e369a1939de0b5c2f89aee6fc2c40b
Merge "Remove race condition (in Networks)"
Merge "Removed duplicate spawn code in PowerVM driver"