Avoid clobbering the --username flag when running add subcommand

[boggsboggs]

Bug is illustrated here:

LDmbp: ~ $ aws-okta add --domain segment.okta.com --username [email protected] -d
Okta password: 

DEBU[0005] domain: segment.okta.com                     
DEBU[0005] Step: 1                                      
DEBU[0005] Failed to validate credentials: Failed to authenticate with okta: &errors.errorString{s:"POST https://segment.okta.com/api/v1/authn: 401 Unauthorized"} 
Failed to validate credentials
LDmbp: ~ $ bash okta.sh 
Which team are you on?
Options are: app, biztech, foundation, personas, platform, product, success
Enter the team based on the table in the setup doc:
foundation
Pulling down /Users/leifdreizler/.aws/config
✔️: Your old aws config has been backed up in /tmp/awsconfig-358d044b5eb575f6b9e5623a20ab5535
✔️: Your aws config was successfully updated.

Respond to the prompts to configure aws-okta
Organization should be "segment"
Region and domain should use the default (us) regardless of whether or not you work in emea
You will need your phone to accept a 2 factor auth push notification
EXAMPLE:
Okta organization: segment
Okta region ([us], emea, preview):
Okta domain [us.okta.com]:
Okta username: [email protected]

Okta organization: segment

Okta region ([us], emea, preview): 

Okta domain [segment.okta.com]: 

Okta password: 

Failed to validate credentials
LDmbp: ~ $ ```

[eculver]

Looks like this was introduced in #137. We should probably have a test for these things 😞

[eculver]

nit: rather than assign it and cause the clobbering at all, you could just inline it:

analyticsClient.Enqueue(analytics.Identify{
    UserId: os.Getenv("USER"),
    Traits: analytics.NewTraits().Set("aws-okta-version", version),
})

[boggsboggs]

agreed that inline is better, I'm going to be lazy and not change it now though

[boggsboggs]

I think this escaped testing because this code only runs when analytics is turned on, and analytics is turned off during testing

[nickatsegment]

This is good stuff.

I say we should encapsulate the analytics logic into its own type. Maybe later.