Use pipes.quote when displaying command

[asottile]

WIP for #845

Some example output:

fix-lint runtests: commands[0] | pre-commit run --all-files --show-diff-on-failure
...
fix-lint runtests: commands[1] | python -c 'print("hint: run /tmp/tox/.tox/fix-lint/bin/pre-commit install to add checks as pre-commit hook")'
...

[codecov]

Codecov Report

Merging #848 into master will increase coverage by <1%.
The diff coverage is 100%.

@@          Coverage Diff           @@
##           master   #848    +/-   ##
======================================
+ Coverage      92%    92%   +<1%     
======================================
  Files          13     13            
  Lines        2414   2415     +1     
  Branches      428    428            
======================================
+ Hits         2214   2215     +1     
  Misses        124    124            
  Partials       76     76