[SPARK-15330][SQL] Implement Reset Command

#### What changes were proposed in this pull request?
Like `Set` Command in Hive, `Reset` is also supported by Hive. See the link: https://cwiki.apache.org/confluence/display/Hive/LanguageManual+Cli

Below is the related Hive JIRA: https://issues.apache.org/jira/browse/HIVE-3202

This PR is to implement such a command for resetting the SQL-related configuration to the default values. One of the use case shown in HIVE-3202 is listed below:

> For the purpose of optimization we set various configs per query. It's worthy but all those configs should be reset every time for next query.

#### How was this patch tested?
Added a test case.

Author: gatorsmile <gatorsmile@gmail.com>
Author: xiaoli <lixiao1983@gmail.com>
Author: Xiao Li <xiaoli@Xiaos-MacBook-Pro.local>

Closes #13121 from gatorsmile/resetCommand.