avocado.utils: Add utils for Avocado debugging

This module should contain useful tools for avocado debugging and
currently contains simple decorator which prints execution
duration of decorated functions and accumulated duration.

This is very easy to use and helpful to compare different versions.

Signed-off-by: Lukáš Doktor <ldoktor@redhat.com>
docs: Add Line-profiler guide

Python's line_profiler is very handy and it might be handy to mention
it in our documentation.

Signed-off-by: Lukáš Doktor <ldoktor@redhat.com>
docs: Add guide to some Eclipse less-known features related to avocado

Signed-off-by: Lukáš Doktor <ldoktor@redhat.com>