Some batcher fixes
Some batcher fixes

Currently the batcher hypervisor parameter must be a dict with one
element (e.g. {"xen-hvm": { "acpi": true }}). This is overly complex and
hard to validate correctly; the patch splits it in two:
  - one "hypervisor" string parameter, with the name of the hypervisor
  - one "hvparams" dictionary, with the hypervisor parameters

The patch also changes the error handling in parsing the definition file
- since this is not a long-running file, we are less concerned with safe
closing of the file, and more with presenting meaningful error
messages.

Reviewed-by: killerfoxi

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