private + readme updates.

gax-java/gax-grpc/src/test/resources/README.md

@@ -1,5 +1,5 @@
-# Generating certificates and keys for testing mTLS-S2A
-Below are the commands which can be used to refresh the certs used in tests. This is the same process
+# Regenerate certificates and keys for testing mTLS-S2A
+Below are the commands which can be used to regenerate the certs used in tests. This is the same process
 used to generate test certs for S2A client in grpc-java: https://github.com/grpc/grpc-java/blob/master/s2a/src/test/resources/README.md
 
 Create root CA

gax-java/gax/src/main/java/com/google/api/gax/rpc/EndpointContext.java

@@ -105,7 +105,7 @@ public static EndpointContext getDefaultInstance() {
   public abstract boolean useS2A();
 
   @Nullable
-  public abstract EnvironmentProvider envProvider();
+  abstract EnvironmentProvider envProvider();
 
   @Nullable
   public abstract String mtlsEndpoint();