[doc] fix cross link between core and plugins doc

For ec2 and s3

docs/reference/modules/discovery/ec2.asciidoc

@@ -1,4 +1,4 @@
 [[modules-discovery-ec2]]
 === EC2 Discovery
 
-EC2 discovery is available as a plugin. See {plugins}/discovery.html#discovery-ec2[discovery-ec2] for more information.
+EC2 discovery is available as a plugin. See {plugins}/discovery-ec2.html[discovery-ec2] for more information.

docs/reference/modules/network.asciidoc

@@ -51,7 +51,7 @@ provided network interface. For example `_en0:ipv4_`.
 provided network interface. For example `_en0:ipv6_`.
 |=======================================================================
 
-When the `cloud-aws` plugin is installed, the following are also allowed
+When the `discovery-ec2` plugin is installed, the following are also allowed
 as valid network host settings:
 
 [cols="<,<",options="header",]

docs/reference/modules/snapshots.asciidoc

@@ -150,7 +150,7 @@ shared file system repository.
 
 Other repository backends are available in these official plugins:
 
-* {plugins}/repository.html#repository-s3[repository-s3] for S3 repository support
+* {plugins}/repository-s3.html[repository-s3] for S3 repository support
 * https://github.com/elasticsearch/elasticsearch-hadoop/tree/master/repository-hdfs[HDFS Plugin] for Hadoop environments
 * https://github.com/elasticsearch/elasticsearch-cloud-azure#azure-repository[Azure Cloud Plugin] for Azure storage repositories