Make min_backoff_ms timeout configurable

[rdsedmundo]

This PR aims to make the variable min_backoff_ms configurable at NodeJS.

Currently, only the max_backoff_ms can be configured individually. And if I'd like to change the max time for a value less than 20 seconds, it didn't work, because the min_backoff_ms will always have precedence, and it's currently forced to 20 seconds.

In a nutshell, this will solve this problem:
http://stackoverflow.com/questions/42256810/how-can-i-change-grpcs-reconnection-behaviour-in-the-node-js-implementation

The answer made by @murgatroid99 didn't work because the min is always 20.

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[grpc-kokoro]

Thanks for your pull request. The automated tests will run as soon as one of the admins verifies this change is ok for us to run on our infrastructure.

[grpc-kokoro]

Thanks for your pull request. The automated tests will run as soon as one of the admins verifies this change is ok for us to run on our infrastructure.

[googlebot]

CLAs look good, thanks!

[grpc-kokoro]

Thanks for your pull request. The automated tests will run as soon as one of the admins verifies this change is ok for us to run on our infrastructure.

[grpc-kokoro]

Thanks for your pull request. The automated tests will run as soon as one of the admins verifies this change is ok for us to run on our infrastructure.

[grpc-kokoro]

Thanks for your pull request. The automated tests will run as soon as one of the admins verifies this change is ok for us to run on our infrastructure.

[grpc-kokoro]

Thanks for your pull request. The automated tests will run as soon as one of the admins verifies this change is ok for us to run on our infrastructure.

[grpc-kokoro]

Thanks for your pull request. The automated tests will run as soon as one of the admins verifies this change is ok for us to run on our infrastructure.

[grpc-kokoro]

Thanks for your pull request. The automated tests will run as soon as one of the admins verifies this change is ok for us to run on our infrastructure.

[grpc-kokoro]

Thanks for your pull request. The automated tests will run as soon as one of the admins verifies this change is ok for us to run on our infrastructure.

[grpc-kokoro]

Thanks for your pull request. The automated tests will run as soon as one of the admins verifies this change is ok for us to run on our infrastructure.

[grpc-kokoro]

Thanks for your pull request. The automated tests will run as soon as one of the admins verifies this change is ok for us to run on our infrastructure.

[grpc-kokoro]

Thanks for your pull request. The automated tests will run as soon as one of the admins verifies this change is ok for us to run on our infrastructure.

[grpc-kokoro]

Thanks for your pull request. The automated tests will run as soon as one of the admins verifies this change is ok for us to run on our infrastructure.

[grpc-kokoro]

Thanks for your pull request. The automated tests will run as soon as one of the admins verifies this change is ok for us to run on our infrastructure.

[murgatroid99]

This is OK to test

[mkvonarx]

What's the status of this PR? I'm also very interested in this feature.

[rdsedmundo]

I've rebased the branch with master.

@murgatroid99 Can you assign @ctiller here? I guess it's better for him to see that.

[grpc-kokoro]

No significant performance differences

[pdf13]

@ctiller can you tell me if this pull request will be released with 1.4.x milestone?