Improve recordset create UI
Improve recordset create UI

The current implementation has '--records' as a quasi-positional
argument, with the nargs='+' parameter it can only be used at the end of
the command, which is confusing to users and doesn't comply with the
help message.

Add a new option '--record' that takes only exactly one record as
parameter and can be repeated when multiple records are present.
Deprecate the old option so it can be removed in the future.

Change-Id: I8fefd9d0f104170d50c5d5dc3cbcc53facda9baf
Closes-Bug: 1736161

openstack/python-designateclient