Use ConsoleIO for output

Using plain `echo` means we still generate output when running `composer install --quiet`.

Simple fix is to use the IO class from the Event (had to pass it to executeBuildBootstrap too for that purpose).
minor #112 Use ConsoleIO for output (dzuelke)

This PR was merged into the 2.3.x-dev branch.

Discussion
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Use ConsoleIO for output

Using plain `echo` means we still generate output when running `composer install --quiet`.

Simple fix is to use the IO class from the Event (had to pass it to `executeBuildBootstrap()` too for that purpose).

Commits
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dabc923 Use ConsoleIO for output
fixed CS