Ensure autogen.sh to be executed at the top-level

The commit adds a test to ensure that user executes
'autogen.sh' at the top-level of the directory.

Signed-off-by: Sahid Orentino Ferdjaoui <sahid.ferdjaoui@cloudwatt.com>
Merge pull request #1822 from sahid/master

Ensure autogen.sh to be executed at the top-level

Reviewed-by: Loic Dachary <loic@dachary.org>