Refactor kernel interface to remove mock and global var

When a unit testing scheme was originally designed for the kernel
interface module in 2017 it was turned into a stateful struct to
accomodate a mock test environment that allowed the tests to call the
real functions and specify what exact commands they expected to be run.

This structure has not been maintained, new tests are not written in
that style and instead use separate testing functions. But the original
tests have not been modified much since that time. Leaving Rita with a
KI global variable that in production doesn't actually do anything all
to support mocking during tests.

This commit removes the mock structure and turns kernel interface into
just a grab bag of utility functions where tests functions are all split
out internally rather than relying on mock.

While we are touching all of these files it will also be renamed to
system_interface rather than kernel interface as we now interface with a
lot more than just linux kernel functions from this module.

althea_kernel_interface/src/babel.rs

@@ -1,7 +1,5 @@
-use crate::KernelInterface;
+use crate::run_command;
 
-impl dyn KernelInterface {
-    pub fn restart_babel(&self) {
-        let _res = self.run_command("/etc/init.d/babeld", &["restart"]);
-    }
+pub fn restart_babel() {
+    let _res = run_command("/etc/init.d/babeld", &["restart"]);
 }

althea_kernel_interface/src/bridge_tools.rs

@@ -1,15 +1,13 @@
 //! Simple helper functions for brctl
 
-use super::KernelInterface;
+use crate::run_command;
 use crate::KernelInterfaceError as Error;
 use std::process::Output;
 
-impl dyn KernelInterface {
-    pub fn add_if_to_bridge(&self, br: &str, iface: &str) -> Result<Output, Error> {
-        self.run_command("brctl", &["addif", br, iface])
-    }
+pub fn add_if_to_bridge(br: &str, iface: &str) -> Result<Output, Error> {
+    run_command("brctl", &["addif", br, iface])
+}
 
-    pub fn del_if_from_bridge(&self, br: &str, iface: &str) -> Result<Output, Error> {
-        self.run_command("brctl", &["delif", br, iface])
-    }
+pub fn del_if_from_bridge(br: &str, iface: &str) -> Result<Output, Error> {
+    run_command("brctl", &["delif", br, iface])
 }

althea_kernel_interface/src/check_cron.rs

@@ -1,19 +1,16 @@
-use super::KernelInterface;
 use crate::KernelInterfaceError as Error;
 use std::process::{Command, Stdio};
 
-impl dyn KernelInterface {
-    /// Checks if the cron service is running and starts it if it's not
-    pub fn check_cron(&self) -> Result<(), Error> {
-        Command::new("/etc/init.d/cron")
-            .args(["enable"])
-            .stdout(Stdio::piped())
-            .output()?;
-        Command::new("/etc/init.d/cron")
-            .args(["start"])
-            .stdout(Stdio::piped())
-            .output()?;
+/// Checks if the cron service is running and starts it if it's not
+pub fn check_cron() -> Result<(), Error> {
+    Command::new("/etc/init.d/cron")
+        .args(["enable"])
+        .stdout(Stdio::piped())
+        .output()?;
+    Command::new("/etc/init.d/cron")
+        .args(["start"])
+        .stdout(Stdio::piped())
+        .output()?;
 
-        Ok(())
-    }
+    Ok(())
 }