Throw exception on odd length Signatures

The old version of this code would silently truncate odd-length
Signatures. However, this masks some bugs. Add a throw of
IllegalArgumentException so users can easily see where they're getting
bad input for Signatures.

Also, go through the existing code and catch this exception or
pre-check the input strings so system_server doesn't crash later.

Bug: 5092338
Change-Id: I8c672c5eaeb738a92c4581ce0df09baf719980ef