test-install: Pass options through to the installer.

This will facilitate testing interesting installer features
using its own CLI.

On my laptop, with a recent base image (updated a few days ago with
`prepare-base`), it takes just 7 or 8 seconds to get to the installer
running, as timed by passing `--help` so that the installer promptly
exits.

tools/test-install/install

@@ -1,7 +1,7 @@
 #!/bin/bash
 
 usage() {
-    echo "usage: install -r RELEASE TARBALL" >&2
+    echo "usage: install -r RELEASE TARBALL [...installer opts..]" >&2
     exit 1
 }
 
@@ -16,6 +16,7 @@ while true; do
     esac
 done
 INSTALLER="$1"; shift
+INSTALLER_ARGS=("$@"); set --
 
 if [ -z "$RELEASE" ] || [ -z "$INSTALLER" ]; then
     usage
@@ -71,7 +72,8 @@ run apt-get install -y curl
 
 <"$INSTALLER" run dd of=/tmp/zulip-server.tar.gz
 run tar -xf /tmp/zulip-server.tar.gz -C /tmp/
-run sh -c '/tmp/zulip-server-*/scripts/setup/install'
+installer_path=$(run sh -c 'echo /tmp/zulip-server-*/scripts/setup/install')
+run "$installer_path" "${INSTALLER_ARGS[@]}"
 # TODO install ends as a zombie (workaround: `sudo ps aux | grep lxc-attach`, kill that)
 
 # TODO settings.py, initialize-database, create realm