Commit transaction in migration

Some databases (e.g., DB2) would deadlock on migration 16 because a
lock was held on the domain table for an uncommitted alter and then
SQLAlchemy queried the domain table info in a separate transaction.

The fix is to commit the ALTER statements to release the lock so
that the domain table schema query will not block.

I've run this with sqlite, mysql, and postgresql and they all worked.

Part of fix for bug 1188785

Change-Id: Ic540a6cb09a0c525df7aaea55b64af96f0dd87c7
add ca_key to sample configuration

this gives end-users a clue that they also have to set
ca_key for using ssl certificates other than the default
place /etc/ssl.

Change-Id: I41c4118d02723730c0ba183add866a0e0fa67e7b
Fixes: Bug #1188956
Merge "add ca_key to sample configuration"
Merge "Commit transaction in migration"