avocado.plugins: Simplify commands --xunit/--json.

Simplify commands for xUnit and JSON output plugins:

* Remove options --xunit-output and --json-output.
* Use '-' to stdout or filename to options --xunit and --json.

Usage examples:

$ avocado --xunit - run sleeptest  # goes to stdout
$ avocado --xunit /tmp/foo.xml run sleeptest
$ avocado --xunit - --json /tmp/foo.json run sleeptest.

Signed-off-by: Ruda Moura <rmoura@redhat.com>
avocado: Fix renamed attribute from avocado.core.output

The reference was incorrect, causing some of the plugins
to crash.

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
Merge pull request #136 from lmr/fix-output

avocado: Fix renamed attribute from avocado.core.output
avocado: Bump to version 0.10.1

Bugfix release.

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
Merge pull request #137 from lmr/version-0-10-1

avocado: Bump to version 0.10.1
Merge pull request #134 from ruda/simplify_cmd_options

avocado.plugins: Simplify commands --xunit/--json.
New feature: silent (human) test result.

Implement new option --silent, to mute the human test result.
It has no effect with --json or --xunit options.

Example:

$ avocado --silent run failtest
$ echo $?
$ 1

Signed-off-by: Ruda Moura <rmoura@redhat.com>