avocado.core.tree: Modify repr() and str() behavior.

To make things easy for debugging, changing the default
behavior of repr() and str() to the class TreeNode.

* For repr() just output the node name.
  Example: TreeNode(name='prod')
* For str() output the node path and the variables from the environment.
  Example: /root/env/prod: foo=123, bar=456

So the output looks like that:

... after a break pointing into the multiplex() function...

(Pdb) print args[0]
[TreeNode(name='short'), TreeNode(name='medium'), TreeNode(name='long'), TreeNode(name='longest')]

(Pdb) print args[0][0]
/root/short: sleep_length=0.5

Signed-off-by: Ruda Moura <rmoura@redhat.com>
avocado.multiplexer: filters accepts strings or lists of strings.

For the filter_only and filter_out functions for filtering,
always accept a string or a list of string for for the parameters.

So this is possible to parse a YAML file like:

foo:
    filter-only: /root/env/prod

or

foo:
    filter-only: [/root/env/prod]

The previous behavior was treating the string as sequence,
so the filters were using the chars as input values.

Signed-off-by: Ruda Moura <rmoura@redhat.com>
avocado.job: better output when variants are zero.

Provide a better output when the number of variants of a multiplex
is zero (for a giving set of tests and one multiplex file).

Also, when there is no tests passed, report early.

Signed-off-by: Ruda Moura <rmoura@redhat.com>
selftests: Unit tests for path_parent() and any_sibling().

Include unit test for support functions used in the multiplexer.py
module: path_parent() and any_sibling().

Signed-off-by: Ruda Moura <rmoura@redhat.com>
multiplexer_unittest.py: simple pep8 style fix

Signed-off-by: Cleber Rosa <crosa@redhat.com>
avocado.multiplexer: improvements in path_parent and any_sibling.

Include documentation for path_parent and any_sibling and
use variable names more relevant.

In function any_sibling, if the number of arguments is less than 2,
then returns False, because it is obviously alone.

Signed-off-by: Ruda Moura <rmoura@redhat.com>
multiplexer_unittest.py: switch from comments to a docstring

Signed-off-by: Cleber Rosa <crosa@redhat.com>
Merge pull request #213 from clebergnu/ruda_multiplex_updates

Ruda's multiplex updates