Ippon response length fix

Ippon Back Power Pro responses are always padded to 64 bytes beyond \r payload terminator. When checking that command was successful (i.e. not echoed back) code relies on the response length reported by blazer_command which will always be 64. To fix this ippon_command should return actual payload length. This change also affects blazer_rating. Currently it assumes that battery voltage should be in %06.2f format, but in reality (and according to documentation) it may also look like %05.2f.