*: do not require env.sh

This removes the need to source env.{sh,fish} when working with hscloud.

This is done by:

 1. Implementing a Go library to reliably detect the location of the
    active hscloud checkout. That in turn is enabled by
    BUILD_WORKSPACE_DIRECTORY being now a thing in Bazel.
 2. Creating a tool `hscloud`, with a command `hscloud workspace` that
    returns the workspace path.
 3. Wrapping this tool to be accessible from Python and Bash.
 4. Bumping all users of hscloud_root to use either the Go library or
    one of the two implemented wrappers.

We also drive-by replace tools/install.sh to be a proper sh_binary, and
make it yell at people if it isn't being ran as `bazel run
//tools:install`.

Finally, we also drive-by delete cluster/tools/nixops.sh which was never used.

Change-Id: I7873714319bfc38bbb930b05baa605c5aa36470a
Reviewed-on: https://gerrit.hackerspace.pl/c/hscloud/+/1169
Reviewed-by: informatic <informatic@hackerspace.pl>
diff --git a/cluster/prodaccess/BUILD.bazel b/cluster/prodaccess/BUILD.bazel
index 6c72082..4db48dd 100644
--- a/cluster/prodaccess/BUILD.bazel
+++ b/cluster/prodaccess/BUILD.bazel
@@ -13,6 +13,7 @@
         "//cluster/certs:go_default_library",
         "//cluster/prodvider/proto:go_default_library",
         "//go/pki:go_default_library",
+        "//go/workspace:go_default_library",
         "@com_github_golang_glog//:go_default_library",
         "@org_golang_google_grpc//:go_default_library",
         "@org_golang_google_grpc//credentials:go_default_library",