tests/vm: add source repos on ubuntu.i386

Possibly because of different behavior on the newly update
cloud-image, trying to run 'apt-get build-dep' results in:

   E: You must put some 'source' URIs in your sources.list

This enables all source repos (even though some are not
needed) for simplicity sake.

Signed-off-by: Cleber Rosa <crosa@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Tested-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20190613130718.3763-5-crosa@redhat.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>

tests/vm/ubuntu.i386

@@ -77,6 +77,7 @@ class UbuntuX86VM(basevm.BaseVM):
         time.sleep(5)
         self.wait_ssh()
         # The previous update sometimes doesn't survive a reboot, so do it again
+        self.ssh_root_check("sed -ie s/^#\ deb-src/deb-src/g /etc/apt/sources.list")
         self.ssh_root_check("apt-get update")
         self.ssh_root_check("apt-get build-dep -y qemu")
         self.ssh_root_check("apt-get install -y libfdt-dev flex bison")