XmlUtils: Add missing readThisByteArrayXml method

Add the missing XML to byte array conversion method.

While there,
1. Fix writeByteArrayXml method to store the hex chars of the value.
2. Cleanup couple of error strings in |readThisIntArrayXml| method.

BUG: 29039296
Change-Id: I6386f7df7c5c8b7bc3bc5a268196da617209cea9
TEST: Compiles & manual testing.