deb: fix OBS build

Add explicit dependency on python3 which is necessary for 'make check'
stage. While at it, add DH_VERBOSE option for debian/control to
facilitate future troubleshooting.

Change-Id: I0ed0bb0f889d4569c9229f3f12ad8bdb11cc1e7c
Related: OS#1948
diff --git a/debian/control b/debian/control
index de7c5e5..766d015 100644
--- a/debian/control
+++ b/debian/control
@@ -8,6 +8,7 @@
                dh-systemd (>= 1.5),
                autotools-dev,
                pkg-config,
+               python3,
                libosmocore-dev,
                libosmo-abis-dev,
                libosmo-netif-dev,