xeanpi: pass network_info to generate_configdrive

Currently network_info is being fetched when generating config drive.
This change ensures the network_info that is already available is
re-used when generating the config_drive.

In addition, it is more consistent to use the network_info that is
passed into this function, rather than potentially lazy loading the
whole info_cache of the instance from the DB, which may not yet be
populated when we are generating the metadata for ConfigDrive anyway.

Fixes bug 1224508
Change-Id: I3e6f5a987593ecd422be61ac50c0d74463ba25d5
Merge "xeanpi: pass network_info to generate_configdrive"