bugfix https and proxy authentication

[slatequarry]

No description provided.

[jvanzyl]

Needs a test, preferably one that shows the issue that your patch fixes. Also you need to match the formatting.

[atanasenko]

This is actually the thing that generates some amount of emails on m2e lists about proxy authentication failures. Here's a corresponding bugzilla [1].
I've checked several versions of okhttp (2.3.0, 2.5.0, 2.7.2 and even latest 3.0.1) and they all just throw an IOException with this message when creating an ssl tunnel to https proxy which returns status 407.

[1] https://bugs.eclipse.org/bugs/show_bug.cgi?id=477893

[atanasenko]

Another fix possibility is adding Proxy-Authentication preemptively.

[jvanzyl]

Fix by @atanasenko with 5b500c6