Add bootstrapping support

Add tools for launching a root shell on the device, and for sending
serial commands to the device. Extend the make.sh script to push those
and configure a root shell. Commands can now be executed as root via:

adb shell rootshell -c \"touch /tmp/test\"

allowing automatic configuration of the tooling.

rootshell/Cargo.toml

@@ -0,0 +1,8 @@
+[package]
+name = "rootshell"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]