Incorrect pipeline total element count for `bst track`

[See original issue on GitLab](https://gitlab.com/BuildStream/buildstream/-/issues/48)
In GitLab by [[Gitlab user @tristanvb]](https://gitlab.com/tristanvb) on Jul 19, 2017, 08:32

When running `bst track` without `--deps all`, the pipeline status area still shows a total element count inclusive of the track target's elements, even though the intention (and behavior) is only to track a single element.

This may also be true in other scenarios like with `bst fetch`, the counter should be changed to be based on the real list of elements which are queued for scheduling.

Start by reproducing the pipeline status area while running `bst track` without `--deps all`, then compare the total with the elements actually queued for scheduling. Check whether the same counting behavior occurs with `bst fetch`; done means the displayed total matches the real scheduled element list in both relevant scenarios.

Written by the indexing model from the issue text.