1. example test uses auto detect flash size. we need to call
`detect_flash_size` before write flash
2. fix incorrect baudrate used: when using WROVER-Kits, it's likely that download with baudrate 921600
will fail. If we don't reset serial setting in decorator, 921600 will
become the default baudrate. This causes all the subsequent
communication fails
3. do hw reset after used esptool function
* Call esptool directly not via subprocess
* Use the same serial port instance for listener thread and esptool
* Includes some refactoring for encapsulation of App vs DUT members
1. replace xunitgen with junit_xml, which can log more info
2. allow test cases to handle junit test report by them own
3. allow test cases to log some info into report via `sysout` tag
