Docs: overhaul of lttng-track(1) and lttng-untrack(1)

Docs: overhaul of lttng-track(1) and lttng-untrack(1)

- Replace the term whitelist by "inclusion set"

  The use of whitelist (and its counterpart, blacklist) is somewhat
  controversial and doesn't align with the terms used in the tracker
  API.

  The "inclusion set" nomenclature is inspired by that used by ACL,
  namely "include list" and "exclude list". Set is preferred to list
  as there is no implied notion of order.

- Adapt process attribute descriptions

  The process attribute descriptions were apparently copy-pasted from
  the original PID description (all are referencing "process IDs").

  A suitable description is added for each process attribute.

- Add new process attributes to lttng-untrack(1)

  The lttng-untrack man page was not updated when the resource types
  introduced in LTTng 2.12 were added to lttng-track(1).

- Group all process attributes with their 'virtual' counter-parts

  The order in which process attributes were described was: pid, uid,
  gid, vpid, vuid, vgid.

  Grouping process attributes with their virtual counterpart (e.g. pid
  followed by vpid) makes it easier to understand the difference at a
  glance.

  The order becomes: pid, vpid, uid, vuid, gid, vgid

- Remove all PID-specific wordings in lttng-untrack(1)

Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Change-Id: I46486c4e90003da3e860682f6c22a0e4a154492b