Fix single quote escaping for python code generator (and its test)

Hard to spot, but in Java the strings "'" and "\'" are identical, so
the implementation and its test were broken identically.

Author: curdbecker

modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractPythonCodegen.java

@@ -214,7 +214,7 @@ public String toDefaultValue(Schema p) {
                 String defaultValue = String.valueOf(p.getDefault());
                 if (defaultValue != null) {
                     defaultValue = defaultValue.replace("\\", "\\\\")
-                            .replace("'", "\'");
+                            .replace("'", "\\'");
                     if (Pattern.compile("\r\n|\r|\n").matcher(defaultValue).find()) {
                         return "'''" + defaultValue + "'''";
                     } else {

modules/openapi-generator/src/test/java/org/openapitools/codegen/python/PythonClientCodegenTest.java

@@ -139,7 +139,7 @@ public void testSingleQuotes() {
         StringSchema schema = new StringSchema();
         schema.setDefault("Text containing 'single' quote");
         String defaultValue = codegen.toDefaultValue(schema);
-        Assert.assertEquals("'Text containing \'single\' quote'", defaultValue);
+        Assert.assertEquals("'Text containing \\'single\\' quote'", defaultValue);
     }
 
     @Test(description = "test backslash default")