contrib: Don't declare OS variable in docker run command (Fixes: #413)

Since the containers are ephemeral just declare directly in the Dockerfile
This also simplifies the run command for users building fwupd

.travis.yml

@@ -17,4 +17,4 @@ install:
   - ./contrib/ci/generate_docker.py
 
 script:
-  - docker run -e OS=$OS -e CI=true -t -v `pwd`/dist:/build/dist fwupd-$OS
+  - docker run -e CI=true -t -v `pwd`/dist:/build/dist fwupd-$OS

contrib/ci/Dockerfile-arch.in

@@ -1,4 +1,5 @@
 FROM archlinux/base
+%%%OS%%%
 ENV LANG en_US.UTF-8
 ENV LC_ALL en_US.UTF-8
 RUN echo fubar > /etc/machine-id

contrib/ci/Dockerfile-debian.in

@@ -1,4 +1,5 @@
 FROM %%%ARCH_PREFIX%%%debian:testing
+%%%OS%%%
 RUN echo fubar > /etc/machine-id
 %%%ARCH_SPECIFIC_COMMAND%%%
 %%%INSTALL_DEPENDENCIES_COMMAND%%%

contrib/ci/Dockerfile-fedora.in

@@ -1,4 +1,5 @@
 FROM fedora:26
+%%%OS%%%
 ENV LANG en_US.UTF-8
 ENV LANGUAGE en_US:en
 ENV LC_ALL en_US.UTF-8

contrib/ci/Dockerfile-ubuntu.in

@@ -1,4 +1,5 @@
 FROM ubuntu:devel
+%%%OS%%%
 RUN echo fubar > /etc/machine-id
 %%%ARCH_SPECIFIC_COMMAND%%%
 %%%INSTALL_DEPENDENCIES_COMMAND%%%

contrib/ci/generate_docker.py

@@ -103,6 +103,8 @@ with open(out.name, 'w') as wfd:
                 wfd.write('RUN cat /etc/apt/sources.list | sed "s/deb/deb-src/" >> /etc/apt/sources.list\n')
                 #add new architecture
                 wfd.write('RUN dpkg --add-architecture %s\n' % SUBOS)
+        elif line == "%%%OS%%%\n":
+            wfd.write("ENV OS %s\n" % TARGET)
         else:
             wfd.write(line)
     wfd.flush()