fixes related to generating creds floppy for imaging worker

- function make_credential_floppy() moved to storage-windows.c
- CC now invokes make_credential_floppy() when creds are supplied
- collapsed cred fields in ncInstance struct into just 'credential' str
- added missing initializers to multiple functions in euca_auth.c

Fixes EUCA-9273
merged from testing, resolved conflict
Merge branch 'dev/dmitrii/vmware-imaging-fixes' into testing