Fix action space path

[erikwijmans]

Motivation and Context

Actually hook-up the greedy follower to the action space path part of the example (this never got done for some reason).

Fixes #111

How Has This Been Tested

Via python examples/example.py --compute_action_shortest_path

Types of changes

• Bug fix (non-breaking change which fixes an issue)

[mathfac]

Looks good, do we have any test for demo runner that can cover this use case?

[erikwijmans]

Added a test

[codecov-io]

Codecov Report

Merging #346 into master will increase coverage by 0.02%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #346      +/-   ##
==========================================
+ Coverage   56.72%   56.74%   +0.02%     
==========================================
  Files         151      153       +2     
  Lines        6740     7038     +298     
==========================================
+ Hits         3823     3994     +171     
- Misses       2917     3044     +127

Impacted Files	Coverage Δ
examples/settings.py	100% <ø> (ø)	⬆️
tests/test_examples.py	100% <100%> (ø)	⬆️
examples/demo_runner.py	49.32% <100%> (ø)
habitat_sim/nav/greedy_geodesic_follower.py	96.22% <100%> (-0.07%)	⬇️
examples/example.py	75.71% <0%> (ø)
habitat_sim/simulator.py	94.17% <0%> (+1.34%)	⬆️

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[mathfac]

Surprised that PR decreases coverage, the follower looks pretty uncovered in master.

[mosra]

Looks like it counts import lines into coverage, and one of these got removed, which makes it a net negative :)

[erikwijmans]

The follower should be really well covered in master: https://github.com/facebookresearch/habitat-sim/blob/master/tests/test_greedy_follower.py

This PR is just hooking it up correctly in the example script