selftests: Add functional tests for --wrapper feature.

Add some functional tests to explore the --wrapper feature.

Signed-off-by: Rudá Moura <rmoura@redhat.com>
docs+man: Add documentation for the --wrapper feature.

Add documentation manual page part for the command line
feature `--wrapper`.

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