Remove providers (#670)

* Move all but mock provider out of tree

These have all been moved to repos under github.com/virtual-kubelet.

* Introduce a providers.Store

This essentially moves the the old register/ handling into a first class
object that can be controlled from the CLI rather than through build
tags deep in the code.

This actually would have made it a bit easier to build the provider
repos and makes the cmd/ code more re-usable.

scripts/process_build_tags.sh

@@ -1,56 +0,0 @@
-#!/bin/bash
-
-# set -e -o pipefail
-
-orig_tags=(${@})
-new_tags=()
-omit_providers=()
-
-let found_provider=0
-
-function debug() {
-	if [ "${V}" = "1" ]; then
-		(>&2 echo "$@")
-	fi
-}
-
-for tag in ${orig_tags[@]}; do
-	case "${tag}" in
-	no_*_provider)
-		# filtered
-		debug "filtered old, invalid ${tag} from tag list, provider is already excluded"
-
-		# store just in case no "proper" provider tags were provided
-		# In such cases we'd build everything, but we don't want to build these
-		p="${tag#no_}"
-		p="${p%_*}"
-		omit_providers+=("${p}")
-		;;
-	*_provider)
-		found_provider+=1
-		new_tags+=("${tag}")
-		;;
-	*)
-		new_tags+=("${tag}")
-		;;
-	esac
-done
-
-if [ ${found_provider} -eq 0 ]; then
-	# include all providers
-	for i in $(ls providers/register/provider_*.go); do
-		p="${i#*provider_}"
-		p="${p%.*}"
-
-		if [[ ! "${omit_providers[*]}" =~ "${p}"  ]]; then
-			debug "including provider ${p}"
-			new_tags+=("${p}_provider")
-		else
-			debug "excluding provider ${p}"
-		fi
-	done
-fi
-
-
-
-echo "${new_tags[@]}"