LUSetInstanceParams: Fix nic handling
LUSetInstanceParams: Fix nic handling

CheckArguments:
  Use constants.VALUE_NONE rather than hardcoding the string "none"
  If we're adding a nic fill the nic_dict with default values
  Check if the mac is syntactically valid, if we have one
  Don't allow the mac to be 'auto' when modifying a nic

CheckPrereq:
  Check that bridge and mac if present in the dict are not None
    (before this wasn't handled at all)
  Generate the nic mac address here if demanded

Exec:
  Do not generate nics and macs

Reviewed-by: iustin


mbakke/ganeti,leshchevds/ganeti,dimara/ganeti,apyrgio/ganeti,ganeti-github-testing/ganeti-test-1,leshchevds/ganeti,yiannist/ganeti,dimara/ganeti,grnet/snf-ganeti,apyrgio/snf-ganeti,mbakke/ganeti,andir/ganeti,grnet/snf-ganeti,apyrgio/ganeti,andir/ganeti,yiannist/ganeti,mbakke/ganeti,onponomarev/ganeti,yiannist/ganeti,bitemyapp/ganeti,ganeti/ganeti,ganeti/ganeti,andir/ganeti,bitemyapp/ganeti,apyrgio/snf-ganeti,leshchevds/ganeti,ganeti/ganeti,ganeti-github-testing/ganeti-test-1,onponomarev/ganeti