Fix Loop in System.Private.Uri

[wtgodbe]

Ports 6da61ff to master

CC @karelz @davidsh

[wtgodbe]

Test failure in System.Net.NetworkInformation.Tests.PingTest/SendPingAsyncWithHostAndTtlAndFragmentPingOptions on OSX10.12:

Assert.Equal() Failure
Expected: Success
Actual: TimedOut

at System.Net.NetworkInformation.Tests.PingTest.PingResultValidator(PingReply pingReply, IPAddress[] localIpAddresses) in /Users/vsts/agent/2.150.3/work/1/s/src/System.Net.Ping/tests/FunctionalTests/PingTest.cs:line 61
at System.Net.NetworkInformation.Tests.PingTest.<>c__DisplayClass46_0.b__1(PingReply pingReply) in /Users/vsts/agent/2.150.3/work/1/s/src/System.Net.Ping/tests/FunctionalTests/PingTest.cs:line 806
at System.Net.NetworkInformation.Tests.PingTest.SendPingAsync(Func2 sendPing, Action1 pingResultValidator) in /Users/vsts/agent/2.150.3/work/1/s/src/System.Net.Ping/tests/FunctionalTests/PingTest.cs:line 776
at System.Net.NetworkInformation.Tests.PingTest.SendPingAsyncWithHostAndTtlAndFragmentPingOptions(Boolean fragment) in /Users/vsts/agent/2.150.3/work/1/s/src/System.Net.Ping/tests/FunctionalTests/PingTest.cs:line 802
--- End of stack trace from previous location where exception was thrown ---

@wfurt is this a known issue on Mac? It seems like it should be unrelated, but I haven't dug further yet.

[wtgodbe]

System.Private.Uri.Functional.Tests: [Long Running Test] 'System.PrivateUri.Tests.IriTest.Iri_ExpandingContents_ThrowsIfTooLong', Elapsed: 00:14:11

This test timed out after 15 minutes on Windows.10.Amd64.ClientRS5.Open-x86:Release. On Debug, the test took about 45 seconds. Looking more now, as this is the test case that was added with this PR

[stephentoub]

Nit: private for both of these

[wtgodbe]

The added test case once again timed out on Windows.10.Amd64.ClientRS5.Open-x86:Release, so it's definitely consistent.