Add HSRP properties question

[arifogel]

• copied from VRRP properties question, except:
  • slightly simpler implementation for populating virtual addresses in answer due to simpler model
    of HsrpGroup vs VrrpGroup

[batfish-bot]

This change is 

[dhalperi]

Reviewed 8 of 8 files at r1, all commit messages.
Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @arifogel and @corinaminer)

a discussion (no related file):
FYI this is likely to cause doc failures in pybatfish. Be prepared :)

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[arifogel]

Reviewed 1 of 1 files at r2.
Reviewable status: all files reviewed (commit messages unreviewed), all discussions resolved (waiting on @corinaminer)

[dhalperi]

Reviewed 1 of 1 files at r2, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @corinaminer)

[arifogel]

Reviewed all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @corinaminer)