Optionally supress sudo rosdep update warning with flag

[ijnek]

This adds a flag to simply supress the warning if a user wants to.
It seems better than telling everyone to ignore the warning if using docker (which is often root).

Resolves: #473

[ijnek]

Mac OS CI failing due to #912

[codecov-commenter]

Codecov Report

❌ Patch coverage is 50.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 74.84%. Comparing base (b6ad189) to head (7150bba).
⚠️ Report is 51 commits behind head on master.

Files with missing lines	Patch %	Lines
src/rosdep2/main.py	50.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #915   +/-   ##
=======================================
  Coverage   74.83%   74.84%           
=======================================
  Files          44       44           
  Lines        3362     3363    +1     
=======================================
+ Hits         2516     2517    +1     
  Misses        846      846           

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