bugfix: Improve support for special characters in schema and table names (#7297)

* Bugfix to SQL Lab to support tables and schemas with characters that require quoting

* Remove debugging prints

* Add uri encoding to secondary tables call

* Quote schema names for presto

* Quote selected_schema on Snowflake, MySQL and Hive

* Remove redundant parens

* Add python unit tests

* Add js unit test

* Fix flake8 linting error

superset/assets/src/SqlLab/actions/sqlLab.js

@@ -285,7 +285,8 @@ export function addTable(query, tableName, schemaName) {
       }),
     );
 
-    SupersetClient.get({ endpoint: `/superset/table/${query.dbId}/${tableName}/${schemaName}/` })
+    SupersetClient.get({ endpoint: encodeURI(`/superset/table/${query.dbId}/` +
+            `${encodeURIComponent(tableName)}/${encodeURIComponent(schemaName)}/`) })
       .then(({ json }) => {
         const dataPreviewQuery = {
           id: shortid.generate(),
@@ -322,7 +323,8 @@ export function addTable(query, tableName, schemaName) {
       );
 
     SupersetClient.get({
-      endpoint: `/superset/extra_table_metadata/${query.dbId}/${tableName}/${schemaName}/`,
+      endpoint: encodeURI(`/superset/extra_table_metadata/${query.dbId}/` +
+          `${encodeURIComponent(tableName)}/${encodeURIComponent(schemaName)}/`),
     })
       .then(({ json }) =>
         dispatch(mergeTable({ ...table, ...json, isExtraMetadataLoading: false })),