Remove accessing cfg.CONF.DATABASE in nec-agent

Fixes bug 1099162

The database configuration was moved to the common DB module.
There no longer needs to access database configuration in the
plugin specific code.

Change-Id: I4b80ea1e84ffa06d0fffa7f8ccdee08a5b77e239
Add exception validation for subnet used.

As a result of bug 1093754 there was no validation of the actual
exception returned.

Change-Id: Ia3104ca523d30ea40c354afa62ed5ce2b88d5b7e
Merge "Remove accessing cfg.CONF.DATABASE in nec-agent"
Merge "Add exception validation for subnet used."