Fix NPE in dump and add additional dump data

This change fixes a NPE when the VcnGatwayConnection attempts to print
for a null underlying network. Additionally, it also prints the existing
configs in order to better identify whether a VCN config is failing to
be privisoned, or failing to start.

Test: manual testing
Change-Id: I44d65633364a5f16d75519cead6729969eb1c06f