Explain plan statement should show plan in WebUi

When explain plan statement is run, the physical plan is generated and returned. However, the plan is not put in the profile and does not show up in the physical plan / visual plan tab in WebUI. If someone wants to look at the visual plan, the only way is to execute the query, which sometime requires long execution time. This makes a bit hard to analyze the plan for a problematic query.

Similar as regular query and CTAS statement, we should put the plan for EXPLAIN PLAN statement, and display properly in WebUi.