runners: esp32.py: Support flashing for MCUboot and IDF bootloader

IDF bootloader requires partition table which is not a requirement for
MCUboot. Hence, esp32.py is updated to flash partition table only if it
exists.

Current implementation only allows flashing zephyr.bin. This commit adds
capability to flash binaries with other names as well
(e.g. - zephyr.signed.bin)

Signed-off-by: Shubham Kulkarni <shubham.kulkarni@espressif.com>