Glider Parser invalid change

[s-pearce]

In the glider parser at these lines:
https://github.com/ooici/marine-integrations/blame/master/mi/dataset/parser/glider.py#L468-L470
The num_hdr_lines variable is not updated as described by the comment. The comment was left from the original implementation of the glider parser code where num_hdr_lines is set as 14 NOMINALLY and then double checked and updated from the num_ascii_tags header value, which tells how many actual lines are in the header.

See original implementation here:
https://github.com/s-pearce/marine-integrations/blob/cgldr/mi/dataset/parser/glider.py#L626-L635

Unless Teledyne Webb Research (the glider vendor) says that glider data files will always and forever have 14 lines in the header (and even then I wouldn't trust it to be true), you may want to include a check of the num_ascii_tags header line to make sure there is 14 lines and update it if not.
-Stuart Pearce