Migration error reporting; fix to EBS rollback code

    - logging when ncClientCall processes do not exit cleanly
    - added some error messages to MigrateInstances, to be returned by NC
    - propagating error messages from CC to CLC and from NC to CC
    - fixed EBS cleanup on rollback; typo fix

    Fixes EUCA-5344, EUCA-5080, EUCA-5806