core: Optional address shuffle in PickFirstLoadBalancer

[temawi]

If provided with the new PickFirstLoadBalancerConfig, PickFirstLoadBalancer will shuffle the list of addresses it receives from the name resolver.

[larry-safran]

Should add tests

• parseLoadBalancingPolicyConfig where enablePickFirstConfig==false and shuffle==true
• picks where enablePickFirstConfig==true and shuffle==false

[temawi]

Should add tests

• parseLoadBalancingPolicyConfig where enablePickFirstConfig==false and shuffle==true
• picks where enablePickFirstConfig==true and shuffle==false

I moved the flag checking to the provider so these exact conditions don't exist in the LB anymore. But I think between the LB and provider tests the bases are covered.

[larry-safran]

You're missing the copyright in the new test file.