DRILL-6863: Drop table is not working if path within workspace starts with "/"
- Made workspace to be honored when table/view name starts with "/" for DROP TABLE, DROP VIEW, CREATE VIEW and SELECT from view queries;
- Made "/{name}" and "{name}" to be equivalent names (the leading "/" is removed) when creating temporary tables so that SELECT ... FROM "/{name}" ... and SELECT ... FROM "{name}" ... produce the same results and behave as regular tables in the context.
closes #1557
