UBUNTU: [debian] do not force do_tools_common

BugLink: http://bugs.launchpad.net/bugs/1764794Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Acked-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

debian/rules

@@ -35,7 +35,7 @@ include $(DROOT)/rules.d/1-maintainer.mk
 
 do_linux_tools=$(sort $(filter-out false,$(do_tools_usbip) $(do_tools_cpupower) $(do_tools_perf) $(do_tools_x86)))
 do_cloud_tools=$(sort $(filter-out false,$(do_tools_hyperv)))
-do_tools_common=true
+do_tools_common?=true
 
 # Don't build tools or udebs in a cross compile environment.
 ifneq ($(DEB_HOST_ARCH),$(DEB_BUILD_ARCH))