engine: Add agent configuration to provider

The Provider entity is being extended with the agent configuration.
The agent configuration represents the specific network agent
configuration and it will be used for installing and configuring the
agent on the installed host.

Change-Id: If93d24404815c080253207f8e9b8f781fac0c7f6
Signed-off-by: Moti Asayag <masayag@redhat.com>