Returns the reference number of the next vgroup if successful and FAIL (or -1) otherwise.
Description
Vgetid sequentially searches the file identified by the parameter file_id and returns the reference number of the vgroup following the vgroup that has the reference number specified by the parameter vgroup_ref.
The search is initiated by calling this routine with a vgroup_ref value of -1. This will return the reference number of the first vgroup in the file. Searching past the last vgroup in the file will cause Vgetid to return FAIL (or -1).