Output (visible) message in case of error (take 2)

[paulo-ferraz-oliveira]

I believe this improves on top of #31, which I found to be too verbose after using it from main.

I've (also, now) tested this with a mix of "dependencies with many tags" and "error for unreachable dependency" and the output is as follows.

➜  test ✗ rebar3 update-deps
===> Analyzing applications...
===> Compiling rebar3_depup
===> Looking for dependencies to update in rebar.config...
===> cowboy can be updated from 2.8.0 to 2.9.0
===> ssh: connect to host <host> port <port>: Operation timed out
fatal: Could not read from remote repository.

Please make sure you have the correct access rights
and the repository exists.
===> Skipping <dep>
===> After applying the changes listed above, don't forget to run rebar3 upgrade.
➜  test ✗