logcat: more error printing clean-up

* The --help text is way too long to print after each error, so simply
  print the errors and exit.
* Report errno in a few cases where it was previously not reported
* Fix more punctuation
* Fix '?' and ':' getopt_long() return cases for long options.

Test: errors look better
Change-Id: I57058a2250e9f3c3431f104e43f0eb5ec60d8c8a