[backport] 👩‍🌾 Make depth camera tests more robust (#897)

[chapulina]

⬅️ Backport

• Backport 👩‍🌾 Make depth camera tests more robust #897
• Address timing issue introduced in Make tests run as fast as possible #1194 (comment)

Note to maintainers: Remember to Merge with commit (not squash-merge or rebase)

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[codecov]

Codecov Report

Merging #1257 (9fbb0f3) into ign-gazebo3 (fe07887) will decrease coverage by 0.00%.
The diff coverage is n/a.

@@               Coverage Diff               @@
##           ign-gazebo3    #1257      +/-   ##
===============================================
- Coverage        77.26%   77.25%   -0.01%     
===============================================
  Files              227      227              
  Lines            13511    13511              
===============================================
- Hits             10439    10438       -1     
- Misses            3072     3073       +1     

Impacted Files	Coverage Δ
src/Server.cc	84.33% <0.00%> (-0.61%)	⬇️

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[Blast545]

LGTM