rustjail: Wrap remaining nix errors with anyhow

Replace `Result` values that use a "bare" `nix` `Error` like this:

```rust
return Err(nix::Error::EINVAL.into());
```

... to the following which wraps the nix` error in an `anyhow` call for
consistency with the other errors returned by `rustjail`:

```rust
return Err(anyhow!(nix::Error::EINVAL));
```

Signed-off-by: James O. D. Hunt <james.o.hunt@intel.com>

src/agent/rustjail/src/cgroups/fs/mod.rs

@@ -174,7 +174,7 @@ impl CgroupManager for Manager {
                 freezer_controller.freeze()?;
             }
             _ => {
-                return Err(nix::Error::EINVAL.into());
+                return Err(anyhow!(nix::Error::EINVAL));
             }
         }
 

src/agent/rustjail/src/container.rs

@@ -1388,13 +1388,13 @@ impl LinuxContainer {
         .context(format!("cannot change onwer of container {} root", id))?;
 
         if config.spec.is_none() {
-            return Err(nix::Error::EINVAL.into());
+            return Err(anyhow!(nix::Error::EINVAL));
         }
 
         let spec = config.spec.as_ref().unwrap();
 
         if spec.linux.is_none() {
-            return Err(nix::Error::EINVAL.into());
+            return Err(anyhow!(nix::Error::EINVAL));
         }
 
         let linux = spec.linux.as_ref().unwrap();

src/agent/rustjail/src/mount.rs

@@ -999,7 +999,7 @@ pub fn finish_rootfs(cfd_log: RawFd, spec: &Spec, process: &Process) -> Result<(
 
 fn mask_path(path: &str) -> Result<()> {
     if !path.starts_with('/') || path.contains("..") {
-        return Err(nix::Error::EINVAL.into());
+        return Err(anyhow!(nix::Error::EINVAL));
     }
 
     match mount(
@@ -1019,7 +1019,7 @@ fn mask_path(path: &str) -> Result<()> {
 
 fn readonly_path(path: &str) -> Result<()> {
     if !path.starts_with('/') || path.contains("..") {
-        return Err(nix::Error::EINVAL.into());
+        return Err(anyhow!(nix::Error::EINVAL));
     }
 
     if let Err(e) = mount(