Allow silencing skip warnings when fetching deps
Allow silencing skip warnings when fetching deps

When fetching deps, if this is a clean repo there will be extensive
messages warning that dependencies which have already been fetched are
being skipped. For large projects being built and tested in a clean
environment this significantly increases the noise level of the build.

This modification adds an additional rebar option
(deps_warning_on_conflict) that will allow disabling these warning
messages. If deps_error_on_conflict is set, an error will still be
thrown. This will not change default behaviour of rebar.

There is a similar outstanding issue:
https://github.com/erlang/rebar3/issues/1105
However this seems to be a push for not outputting warnings when the dep
version is the same, rather than disabling warnings altogether.

saleyn/rebar3,rebar/rebar3,djnym/rebar3,lrascao/rebar3,vladdu/rebar3,rebar/rebar3,tsloughter/rebar3,erlang/rebar3,ferd/rebar3