Add dockerfiles for the conda package builds (#3344)

Add dockerfiles for the conda package builds (#3344)

* First shot

* Add dockerfile for CPU too

* Finish the build infrastructure

* Remove extra file

* Comment out the Jenkinsfile section since it is not ready

* Add missing license headers

* Update to newer cudnn that anaconda packaged

* Bump the build numbers for the newer cudnn

* Bring back the toolchain option with a tweak for cuda

* Cache some large packages in the docker and update to llvm 7.0.0

* Merge all the python packages together

* First fix for the conda cuda builds (again)

* Use the tarball version of cudnn since tvm has trouble detecting the other one

* Use llvm 8.0 from the numba packages

* Also use llvm 8.0 for the cpu builds

* Don't use the anaconda compiler for OS X

* Enable Metal on OS X builds

* Make sure to detect undefined variables in scripts

* Fix build when not using cuda