Read TOXIPROXY_* environment variables if they exist as default values for the hostname

[maaslalani]

This PR introduces reading from the TOXIPROXY_URL variable (or TOXIPROXY_HOST + TOXIPROXY_PORT) as defaults rather than needing to pass in the -h somehost.railgun:8474 each time any command is run.

No variable exported

This tries to read the normal fallback url and cannot connect since I don't have toxiproxy running on this url.

$ go run cli/cli.go list
Failed to retrieve proxies: Get "http://localhost:8474/proxies": dial tcp 127.0.0.1:8474: connect: connection refused
exit status 1

Variable exported

Connects to the correct host without the extra flags, even though it is not 127.0.0.1:8474 since the TOXIPROXY_URL is set.

$ export TOXIPROXY_URL="http://somehost.railgun:8474"
$ go run cli/cli.go list
Name                    Listen          Upstream                Enabled         Toxics
======================================================================================
mysql                   192.168.64.48:30500     somehost.railgun:3306        enabled         1

Hint: inspect toxics with `toxiproxy-cli inspect <proxyName>`

[miry]

@maaslalani Hi. It looks ok. Did you check the feature of urfave/cli to read values from ENVs: https://github.com/urfave/cli/blob/master/docs/v2/manual.md#values-from-the-environment?

Would it better to have the framework handle all configurations?

[maaslalani]

@maaslalani Hi. It looks ok. Did you check the feature of urfave/cli to read values from ENVs: https://github.com/urfave/cli/blob/master/docs/v2/manual.md#values-from-the-environment?

Would it better to have the framework handle all configurations?

Ah no I didn't, I'll change this up to do that, sounds like a much better approach, thanks!

[maaslalani]

@miry Updated this PR, using the EnvVars is much better 👍 Thanks for the suggestion.

[miry]

@maaslalani Pls update changelog.