Migrate data from cap_port_filter to vif_details

There was introduced a new column vif_details for ml2_port_binding table
and dropped cap_port_filter column. Data was lost during the migration
causing no data in vif_details.

This patch transforms data from cap_port_filter to vif_details column as
a part of db migration. MigrationContext.execute() calls underlaying
methods depending whether migration is online or offline therefore data
are migrated in offline migration too.

Partial-bug: #1235149
Change-Id: Icc5dc6e8221a542f5190d0222ac4d10197d15ac1
Merge "Migrate data from cap_port_filter to vif_details"