Reduce input size in some tests (#890)

Motivation:

Now that we have TSAN enabled in CI, some tests take an unreasonably
long time to complete. As a result of this CI often takes over 30
minutes to complete.

Modifications:

- Reduce the input size for the slowest tests

Result:

- Faster CI

Tests/GRPCTests/FunctionalTests.swift

@@ -32,7 +32,7 @@ class FunctionalTestsInsecureTransport: EchoTestCaseBase {
   }
 
   var lotsOfStrings: [String] {
-    return (0..<5_000).map {
+    return (0..<500).map {
       String(describing: $0)
     }
   }
@@ -61,7 +61,7 @@ class FunctionalTestsInsecureTransport: EchoTestCaseBase {
 
     // Sending that many requests at once can sometimes trip things up, it seems.
     let clockStart = clock()
-    let numberOfRequests = 2_000
+    let numberOfRequests = 200
 
     // Due to https://github.com/apple/swift-nio-http2/issues/87#issuecomment-483542401 we need to
     // limit the number of active streams. The default in NIOHTTP2 is 100, so we'll use it too.
@@ -90,7 +90,7 @@ class FunctionalTestsInsecureTransport: EchoTestCaseBase {
         get.status.map { $0.code }.assertEqual(.ok, fulfill: statusExpectation)
       }
 
-      if upperBound % 1_000 == 0 {
+      if upperBound % 100 == 0 {
         print("\(upperBound) requests sent so far, elapsed time: \(Double(clock() - clockStart) / Double(CLOCKS_PER_SEC))")
       }