helper functions: improve append_hostname() and sort_nodes()

[cmoussa1]

Problem

The function descriptions for append_hostname() and sort_nodes() could use some better descriptions. sort_nodes() as a whole could probably use some improvement via condensing it down.

---

This PR edits the descriptions for both helper functions and remove the extra whitespace between the function description and the start of the function definition.

Specifically, in sort_nodes():

• simplify the string processing by checking "nodelist" directly
  instead of assigning it to another variable.
• add an extract_key() function to extract the prefix, numeric part,
  and suffix using regex and return a tuple of it.
• use the returned tuple from extract_key() to sort the original
  nodelist by prefix, numeric part, and suffix.