[sonic_eeprom] Make compatible with Python 2 and 3 (sonic-net#127)

The `string` type has changed between Python 2 and 3. Therefore, the Python 3 version of this library is broken.

This PR changes the data type of the raw EEPROM data to a `bytearray`, which is treated the same in both Python 2 and Python 3, and is technically a more appropriate data type for the raw bytes anyway.

However, this PR could cause issues if any vendors are overriding the `read_eeprom_bytes()` or `read_eeprom()` functions and returning a `string`. Any vendors doing so will need to refactor their implementation to return a `bytearray` instead.

sonic_platform_base/sonic_eeprom/eeprom_base.py

@@ -101,12 +101,12 @@ def compute_2s_complement(self, e, size):
     def compute_dell_crc(self, message):
         poly = 0x8005
         reg = 0x0000
-        message += '\x00\x00'
+        message += bytearray(b'\x00\x00')
         for byte in message:
             mask = 0x80
             while (mask > 0):
                 reg<<=1
-                if ord(byte) & mask:
+                if byte & mask:
                     reg += 1
                 mask>>=1
                 if reg > 0xffff:
@@ -265,7 +265,7 @@ def read_eeprom_bytes(self, byteCount, offset=0):
             if F is not None:
                 F.close()
 
-        return o
+        return bytearray(o)
 
     def read_eeprom_db(self):
         return 0