[Credo][Ycable] enhancement and error exception for some APIs (sonic-…

…net#303)

Description
fix the switch_count_tor_a() will always clear the counter after read issue.
use YCable.EEPROM_ERROR due to the definition was moved.
check and activate firmware by the inactive firmware version individually.
add more error exception for activate_firmware()
authored-by evan-lin xinyu0123@gmail.com

Signed-off-by: vaibhav-dahiya vdahiya@microsoft.com