DRILL-7261: Simplify Easy framework config for new scan

Most format plugins are created using the Easy format plugin. A recent
change added support for the "row set" scan framework. After converting
the text and log reader plugins, it became clear that the setup code
could be made simpler.

* Add the user name to the "file scan" framework.
* Pass the file system, split and user name to the batch reader via
  the "schema negotiator" rather than via the constructor.
* Create the traditional "scan batch" scan or the new row-set scan via
  functions instead of classes.
* Add Easy config option and method to choose the kind of scan
  framework.
* Add Easy config options for some newer options such as whether the
  plugin supports statistics.

Simplified reader creation

* The batch reader can be created just by overriding a method.
* A default error context is provided if the plugin does not provide
  one.

Tested by running all unit tests for the CSV reader which is based on
the new framework, and by testing the converted log reader (that reader
is not part of this commit.)

closes #1796

exec/java-exec/src/main/java/org/apache/drill/exec/physical/impl/scan/file/FileScanFramework.java

@@ -62,7 +62,8 @@
 
 public class FileScanFramework extends ManagedScanFramework {
 
-  private static final org.slf4j.Logger logger = org.slf4j.LoggerFactory.getLogger(FileScanFramework.class);
+  private static final org.slf4j.Logger logger =
+      org.slf4j.LoggerFactory.getLogger(FileScanFramework.class);
 
   /**
    * The file schema negotiator adds no behavior at present, but is
@@ -80,7 +81,6 @@ public interface FileSchemaNegotiator extends SchemaNegotiator {
     /**
      * Gives the Drill file system for this operator.
      */
-
     DrillFileSystem fileSystem();
 
     /**
@@ -186,6 +186,10 @@ public ManagedReader<? extends SchemaNegotiator> next() {
       return newReader();
     }
 
+    public CustomErrorContext errorContext() {
+      return fileFramework == null ? null : fileFramework.errorContext();
+    }
+
     public abstract ManagedReader<? extends FileSchemaNegotiator> newReader();
   }
 

exec/java-exec/src/main/java/org/apache/drill/exec/physical/impl/scan/framework/ManagedScanFramework.java

@@ -135,10 +135,17 @@ public interface ReaderFactory {
 
   public static class ScanFrameworkBuilder extends ScanOrchestratorBuilder {
     protected ReaderFactory readerFactory;
+    protected String userName;
 
     public void setReaderFactory(ReaderFactory readerFactory) {
       this.readerFactory = readerFactory;
     }
+
+    public ReaderFactory readerFactory() { return readerFactory; }
+
+    public void setUserName(String userName) {
+      this.userName = userName;
+    }
   }
 
   // Inputs

exec/java-exec/src/main/java/org/apache/drill/exec/physical/impl/scan/framework/SchemaNegotiator.java

@@ -64,8 +64,15 @@ public interface SchemaNegotiator {
    * Specify an advanced error context which allows the reader to
    * fill in custom context values.
    */
+
   void setErrorContext(CustomErrorContext context);
 
+  /*
+   * The name of the user running the query.
+   */
+
+  String userName();
+
   /**
    * Specify the table schema if this is an early-schema reader. Need
    * not be called for a late-schema readers. The schema provided here,

exec/java-exec/src/main/java/org/apache/drill/exec/physical/impl/scan/framework/SchemaNegotiatorImpl.java

@@ -100,6 +100,11 @@ public void setBatchSize(int maxRecordsPerBatch) {
     batchSize = maxRecordsPerBatch;
   }
 
+  @Override
+  public String userName() {
+    return framework.builder.userName;
+  }
+
   /**
    * Callback from the schema negotiator to build the schema from information from
    * both the table and scan operator. Returns the result set loader to be used