neutron_metadata_proxy_shared_secret should not be written to log file

This patch sets secret=True for the following config option
neutron_metadata_proxy_shared_secret

Change-Id: I381ea9e89f76beac11b03def6e3ccfee2a55e48f
Closes-bug: #1288463
VMware: raise an exception for unsupported disk formats

At the moment 'vmdk' and 'iso' are the only disk formats supported.
If an invalid format is passed with the image then the driver will
throw and exception.

Change-Id: I834856f33a0644bc03b89a2b98e4e188c112e338
Closes-bug: #1287844
Make linux_net use objects for last fixed ip query

This converts the final uses of direct database calls from the
linux_net module by utilizing the calls just added to the
FixedIP object.

Related to blueprint nova-network-objects

Related-bug: 1290568
Change-Id: I58828e9112e43967fe8daa070575ca122041690a
Merge "Make linux_net use objects for last fixed ip query"
Merge "neutron_metadata_proxy_shared_secret should not be written to log file"
Merge "VMware: raise an exception for unsupported disk formats"