[Event Hubs Client] Tracks One and Two (Test Stability Tweaks)

- Allowing slower backoff and higher jitter to account for the management plane
  behavior under load.  The management plane appears to have difficulty recovering
  after the first problem is encountered.  The hope is that giving it more time to
  recover and lowering the concurrent calls by randomzing retry times will help.

- Marking two tests in the track one library to be skipped, as they've been
  consistently unstable during nightly runs.  (tracking under Azure#7435)

sdk/eventhub/Azure.Messaging.EventHubs/tests/Infrastructure/EventHubScope.cs

@@ -31,10 +31,10 @@ public sealed class EventHubScope : IAsyncDisposable
         private const int RetryMaximumAttemps = 15;
 
         /// <summary>The number of seconds to use as the basis for backing off on retry attempts.</summary>
-        private const double RetryExponentialBackoffSeconds = 1.5;
+        private const double RetryExponentialBackoffSeconds = 2.0;
 
         /// <summary>The number of seconds to use as the basis for applying jitter to retry back-off calculations.</summary>
-        private const double RetryBaseJitterSeconds = 7.0;
+        private const double RetryBaseJitterSeconds = 8.0;
 
         /// <summary>The buffer to apply when considering refreshing; credentials that expire less than this duration will be refreshed.</summary>
         private static readonly TimeSpan CredentialRefreshBuffer = TimeSpan.FromMinutes(5);

sdk/eventhub/Microsoft.Azure.EventHubs/tests/Client/MiscTests.cs

@@ -160,7 +160,7 @@ public async Task ClosingReceiverEntity()
             }
         }
 
-        [Fact]
+        [Fact(Skip = "Test is unstable during nightly runs.  Tracking with #7435")]
         [LiveTest]
         [DisplayTestMethodName]
         public async Task ClosingEventHubClientClosesSenderEntities()
@@ -178,7 +178,7 @@ public async Task ClosingEventHubClientClosesSenderEntities()
             }
         }
 
-        [Fact]
+        [Fact(Skip = "Test is unstable during nightly runs.  Tracking with #7435")]
         [LiveTest]
         [DisplayTestMethodName]
         public async Task ClosingEventHubClientClosesReceiverEntities()

sdk/eventhub/Microsoft.Azure.EventHubs/tests/Infrastructure/EventHubScope.cs

@@ -24,8 +24,8 @@ namespace Microsoft.Azure.EventHubs.Tests
     internal sealed class EventHubScope : IAsyncDisposable
     {
         private const int RetryMaximumAttemps = 15;
-        private const double RetryExponentialBackoffSeconds = 1.5;
-        private const double RetryBaseJitterSeconds = 7.0;
+        private const double RetryExponentialBackoffSeconds = 2.5;
+        private const double RetryBaseJitterSeconds = 8.0;
 
         private static readonly TimeSpan CredentialRefreshBuffer = TimeSpan.FromMinutes(5);
         private static readonly ThreadLocal<Random> RandomNumberGenerator = new ThreadLocal<Random>(() => new Random(Interlocked.Increment(ref s_randomSeed)), false);