*: 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/env.sh b/env.sh
index e9cfd22..0723030 100644
--- a/env.sh
+++ b/env.sh
@@ -1,23 +1,24 @@
-# source me to have all the nice things
+# Source this file to have hscloud tools available in your PATH after running
+# `bazel run //tools:install`.
 
 if [ "$0" == "$BASH_SOURCE" ]; then
     echo "You should be sourcing this."
     exit 1
 fi
 
-export hscloud_root="$( cd "$(dirname "$BASH_SOURCE")"; pwd -P )"
-
+hscloud_root="$( cd "$(dirname "$BASH_SOURCE")"; pwd -P )"
 if [ ! -f "$hscloud_root/WORKSPACE" ]; then
     echo "Could not find WORKSPACE"
     exit 1
 fi
-
 hscloud_path="$hscloud_root/bazel-bin/tools:$hscloud_root/bazel-bin/cluster/tools"
-
 [[ ":$PATH:" != *":$hscloud_path:"* ]] && PATH="$hscloud_path:${PATH}"
+unset -f hscloud_root
+unset -f hscloud_path
 
+# Leftover junk. This should be removed, as env.sh is now optional.
+# Do _not_ add more aliases!
 alias bajzel=bazel
-
 gpg-unlock() {
     echo "test" | gpg2 --sign --batch --no-tty -o /dev/null
 }