Since Python3 handles encoding differently than Python2,
a change in the way the data is encoded and sent to the target is needed.
1. Change the test data to be sent as hex string
2. Convert the characters to binary bytes.
This is done because the mbed tools translate the encoding differently
(mbed-greentea, and mbed-htrunner)
Fix parsing error that contains special character.
The previous implementation replaced the `:` char with `\n`,
and split on `\n`. Test data containing strings with `\n`
were split as well. Fixes#2193.
The split function caused strings containing `\:` to add
another escape char, resulting in `\\:`. This caused the
tests with the `\:` in the string data to fail.
The fix doesn't replace with `\n`, but splits all `:` that
are not preceded with `\`. After that, removes the preceding `\` char.
