feat: Allow triggering a release via the contrib/release script

- Requires docker, git, and package_cloud gems
- Requires the PACKAGECLOUD_API_TOKEN environment variable
- Builds both a deb and rpm, pushing both to packagecloud
- Upgrades the golang build environment to 1.7.5
- Combines both build Dockerfiles into a single, generic env
- Fixes issue where internal-functions file for tar plugin was not executable
- Ensures that built plugins have a callback to clean up their source files before packaging
- Adds support for “betafish” releases, which are untested versions of Dokku that are available via a separate packagecloud repository.

deb.mk

@@ -140,16 +140,16 @@ endif
 ifneq (,$(findstring false,$(IS_RELEASE)))
 	sed -i.bak -e "s/^/`date +%s`:/" /tmp/build/var/lib/dokku/STABLE_VERSION && rm /tmp/build/var/lib/dokku/STABLE_VERSION.bak
 endif
-	rm /tmp/build/DEBIAN/lintian-overrides
-	mv debian/lintian-overrides /tmp/build/usr/share/lintian/overrides/dokku
+	rm -f /tmp/build/DEBIAN/lintian-overrides
+	cp debian/lintian-overrides /tmp/build/usr/share/lintian/overrides/dokku
 ifdef DOKKU_GIT_REV
 	echo "$(DOKKU_GIT_REV)" > /tmp/build/var/lib/dokku/GIT_REV
 else
 	git rev-parse HEAD > /tmp/build/var/lib/dokku/GIT_REV
 endif
-	sed -i "s/^Version: .*/Version: `cat /tmp/build/var/lib/dokku/STABLE_VERSION`/g" /tmp/build/DEBIAN/control
-	dpkg-deb --build /tmp/build "/tmp/dokku_`cat /tmp/build/var/lib/dokku/STABLE_VERSION`_$(DOKKU_ARCHITECTURE).deb"
-	lintian "/tmp/dokku_`cat /tmp/build/var/lib/dokku/STABLE_VERSION`_$(DOKKU_ARCHITECTURE).deb"
+	sed -i.bak "s/^Version: .*/Version: `cat /tmp/build/var/lib/dokku/STABLE_VERSION`/g" /tmp/build/DEBIAN/control && rm /tmp/build/DEBIAN/control.bak
+	dpkg-deb --build /tmp/build "/tmp/dokku_`cat /tmp/build/var/lib/dokku/VERSION`_$(DOKKU_ARCHITECTURE).deb"
+	lintian "/tmp/dokku_`cat /tmp/build/var/lib/dokku/VERSION`_$(DOKKU_ARCHITECTURE).deb"
 
 deb-plugn:
 	rm -rf /tmp/tmp /tmp/build $(PLUGN_PACKAGE_NAME)