fix: make src install less verbose

[daenny]

I have some custom .rdmanifest which install from source. Now the script is always printed in terminal (even with rosdep -q)
I think, this should be debug information.

[tfoote]

This looks reasonable to me. Though in general when running potentially arbitrary scripts I'd prefer them to be at least seen once. But yes if the user wants a quiet output then we should let them suppress this.

[tfoote]

The CI appears to be failing due to python hard deprecating yaml_load we worked around the externally accessible instances in #651 but left some internal ones.

[codecov-io]

Codecov Report

Merging #675 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master     #675   +/-   ##
=======================================
  Coverage   75.19%   75.19%           
=======================================
  Files          30       30           
  Lines        2890     2890           
=======================================
  Hits         2173     2173           
  Misses        717      717

Impacted Files	Coverage Δ
src/rosdep2/platforms/source.py	90.5% <100%> (ø)	⬆️
src/rosdep2/shell_utils.py	100% <100%> (ø)	⬆️
src/rosdep2/sources_list.py	85.91% <100%> (ø)	⬆️

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[daenny]

I added a commit which replaces the remaining yaml.load() with yaml.safe_load()

[tfoote]

Thanks!