Bump to 3.4.0

Patches:

- Try to start epmd when distribution fails
- Allow non-default profile deps upgrade
- Switch default license in templates to Apache 2.0, and hook it up in
  the .app file
- Fix git SHA comparisons for dep update
- Let relx know about rebar-specified erl_opts
- Use rm_rf instead of ec_file:delete, fixing some deps-related issues
  on Windows
- Handle internal CT failures
- Fix profile merging of erl_first_files options
- Fix CT output in skipped test cases and failing end of function
  hooks
- Officially drop R15 support, since its SSL libs can no longer talk
  to hex.pm
- REBAR_COLOR supports all ec_cmd_log intensity options, allowing the
  none value to disable all colors without dropping termcap support
- Bump relx to 3.22.4

The one new feature supported here is for the interactive shell:

- Support commands in the shell such as r3:Command(),
  r3:Command("--args=as a string"), or r3:Command(Namespace, "--args=as a
  string"), instead of just r3:do(Command).

bootstrap

@@ -24,7 +24,7 @@ main(_) ->
     bootstrap_rebar3(),
 
     %% Build rebar.app from rebar.app.src
-    {ok, App} = rebar_app_info:new(rebar, "3.3.6", filename:absname("_build/default/lib/rebar/")),
+    {ok, App} = rebar_app_info:new(rebar, "3.4.0", filename:absname("_build/default/lib/rebar/")),
     rebar_otp_app:compile(rebar_state:new(), App),
 
     %% Because we are compiling files that are loaded already we want to silence

src/rebar.app.src

@@ -3,7 +3,7 @@
 
 {application, rebar,
  [{description, "Rebar: Erlang Build Tool"},
-  {vsn, "git"},
+  {vsn, "3.4.0"},
   {modules, []},
   {registered, []},
   {applications, [kernel,