[build]: add debug info for dpkg frontend lock (#8375)

print out the process that hold the dpkg frontend lock.

Signed-off-by: Guohan Lu <lguohan@gmail.com>

slave.mk

@@ -541,7 +541,7 @@ $(SONIC_INSTALL_DEBS) : $(DEBS_PATH)/%-install : .platform $$(addsuffix -install
 			{ while dpkg -s $(firstword $(subst _, ,$(basename $(deb)))) | grep "^Version: $(word 2, $(subst _, ,$(basename $(deb))))" &> /dev/null; do echo "waiting for $(deb) to be uninstalled" $(LOG); sleep 1; done } )
 		# put a lock here because dpkg does not allow installing packages in parallel
 		if mkdir $(DEBS_PATH)/dpkg_lock &> /dev/null; then
-			{ sudo DEBIAN_FRONTEND=noninteractive dpkg -i $(DEBS_PATH)/$* $(LOG) && rm -d $(DEBS_PATH)/dpkg_lock && break; } || { rm -d $(DEBS_PATH)/dpkg_lock && exit 1 ; }
+			{ sudo DEBIAN_FRONTEND=noninteractive dpkg -i $(DEBS_PATH)/$* $(LOG) && rm -d $(DEBS_PATH)/dpkg_lock && break; } || { rm -d $(DEBS_PATH)/dpkg_lock && sudo lsof /var/lib/dpkg/lock-frontend && ps aux && exit 1 ; }
 		fi
 	done
 	$(FOOTER)