Avocado: Add htmlresult plugin

Add a plugin to write a job summary HTML page.
The plugin takes results and creates a JSON context, that
is used by the pystache library, to render an HTML page
using a mustache template.

This commit contains the base plugin code, and the resource
files used by the plugin (bootstrap for some of the js, base
css, datatables for the test results table functionality).

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
avocado.job: If possible, write an HTML report at the job results dir

If the HTML plugin is enabled on this install, write a
report at html/ on that job results directory. This will
help people to read avocado test results on a portable
and pleasant way.

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
setup.py: Add plugin resource files

Package plugin resource files, as they're necessary to
the given plugin's functionality. Update MANIFEST.in
with the new data dir.

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
avocado.spec: Add subpackage plugins-output-html

Add a subpackage plugins-output-html, that will turn
HTML functionality optional in avocado. This way
we don't force people to install unnecessary dependencies
for the functionality they actually want.

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>