IMP-1291: Support "extended" ASCII characters as delimiters in text files

This fixes how we validate delimiters to be in line with Hive. A delimiter must
fit in a single byte and can be specified in the following formats, as far as I can
tell (there isn't documentation):
- A single ASCII or unicode character (ex. '|')
- An escape character in octal format (ex. \001. Stored in the metastore as a
  unicode character: \u0001).
- A signed decimal integer in the range [-128:127]. Used to support delimiters
  for ASCII character values between 128-255 (-2 maps to ASCII 254).

Previously, we were not handling the "signed integer" case so there was no way
to specify a delimiter in the "extended" ASCII range of 128-255.

To support result validation, the test infrastructure had to be updated to support
reading/writing different character encodings.

Change-Id: Ie3c4d444dc9c6e60192093ed0c0f6f151eab16bc
Reviewed-on: http://gerrit.ent.cloudera.com:8080/1848
Reviewed-by: Lenni Kuff <lskuff@cloudera.com>
Tested-by: jenkins