rest: extract elements instead of matching

[jkoelker]

If the host has old style VIPs, then the matching will fail, instead
just extract the first two elements regardless of the length.

dcos/dcos#7568

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 66.05%. Comparing base (d35033b) to head (63cc66a).
⚠️ Report is 5 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #199      +/-   ##
==========================================
+ Coverage   66.02%   66.05%   +0.02%     
==========================================
  Files          55       55              
  Lines        3759     3759              
==========================================
+ Hits         2482     2483       +1     
+ Misses       1277     1276       -1     

Flag	Coverage Δ
ct	34.66% <ø> (ø)
ct2	46.02% <ø> (+0.02%)	⬆️
eunit	24.79% <ø> (ø)

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Files with missing lines	Coverage Δ
apps/dcos_rest/src/dcos_rest_vips_handler.erl	45.00% <ø> (ø)

... and 1 file with indirect coverage changes

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