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
Merge "neutron_metadata_proxy_shared_secret should not be written to log file"
Merge "VMware: raise an exception for unsupported disk formats"