Support --extra_args parameter in dev/run

[iilyak]

Overview

Sometimes there is a need to specify additional arguments for the beam process we start from dev/run.
In particular the feature is handy for:

• changing emulator flags
• simulate OOM via available RAM restrictions
• enable module loading tracing
• configure number of schedulers
• modify applications configuration
• run customization script to add extra development deps (such as automatic code reload)

Historically developers had to edit dev/run to do it.
This PR adds an ability to specify additional arguments via --extra_args argument.

In order to run customization script create customization.erl which exports start/0 and run it using:

dev/run --extra_args='-run customization'

Testing recommendations

1. Create dev/customization.erl with the following content:

   -module(customization).
   
   -export([start/0]).
   
   start() ->
     error_logger:info_msg("CUSTOMIZATION!!!~n").
   

2. run dev/run --extra_args='-run customization'
3. check logs and verify there is a line similar to the following

   [info] 2019-09-10T12:17:00.828103Z node1@127.0.0.1 <0.5.0> -------- CUSTOMIZATION!!!
   

Related Issues or Pull Requests

Checklist

• Code is written and works correctly
• Changes are covered by tests
• Any new configurable parameters are documented in rel/overlay/etc/default.ini
• A PR for documentation changes has been made in https://github.com/apache/couchdb-documentation