Fix `cake bake fixture` failing.

Bake failed as the connection property was not properly copied over in
sub-tasks. This fixes that issue by setting the property from params on
initialize().

Refs #3638
Fix DateTimeTime breaking on timestamp values.

Since we don't have a separate TimestampType the DateTimeType needs to
handle integer values (timestamps).
Merge pull request #3639 from cakephp/3.0-bake-connection

3.0 bake connection