DRILL-392: Support SHOW TABLES/SCHEMAS and DESCRIBE TABLE.

Use Optiq parser template to generate Drill parser
a) exec/java-exec/pom.xml changes:
   1. Write a plugin to move current existing codegen directory to target
      (fmpp can't handle more than one directory as template input dir).
   2. Change template directory path in fmpp plugin.
   3. Extract CombinedParser.jj into target/codegen/templates directory.
   4. Plugin to compile CombinedParser.jj using javacc.

b) Add parser.tdd to define values for freemarker variables in CombinedParser.jj template.
c) Define grammar and SqlCall types for new DDL statements.
d) Handlers to rewrite newly added SqlCall DDL statements as select queries from INFORMATION_SCHEMA.