Flash and monitor commands do not use the same baudrate source

[SergioGasquez]

The flash command has a --monitor-baud option and does not use the env:ESPFLASH_BAUD. The monitor command has a --baud option that does use the env:ESPFLASH_BAUD.

In esptool/esp-idf-monitor they use ESPTOOL_BAUD for setting the flashing baudrate and then IDF_MONITOR_BAUD/MONITORBAUD for setting the monitoring baudrate

We should probably do something about this, either we make ESPFLASH_BAUD set the monitoring baudrate in all the commands or have another environment variable to set the monitoring baudrate. Id go for the later one.