Actually run shell-lint on tools

Makefile

@@ -102,6 +102,7 @@ tests: $(SCOPE_BACKEND_BUILD_UPTODATE)
 
 lint: $(SCOPE_BACKEND_BUILD_UPTODATE)
 	./tools/lint -ignorespelling "agre " -ignorespelling "AGRE " .
+	./tools/shell-lint tools
 
 prog/static.go: $(SCOPE_BACKEND_BUILD_UPTODATE)
 	esc -o $@ -prefix client/build client/build

backend/Dockerfile

 FROM golang:1.6.2
 RUN apt-get update && \
-	apt-get install -y libpcap-dev python-requests time file && \
+	apt-get install -y libpcap-dev python-requests time file shellcheck && \
 	rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/*
 RUN go clean -i net && \
 	go install -tags netgo std && \