daemon: Daemon.getIpcContainer: make errors less repetitive

- Most error-message returned would already include "container" and the
  container ID in the error-message (e.g. "container %s is not running"),
  so there's no need to add a custom prefix for that.
- os.Stat returns a PathError, which already includes the operation ("stat"),
  the path, and the underlying error that occurred.

And while updating, let's also fix the name to be proper camelCase :)

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

daemon/oci_linux.go

@@ -292,9 +292,9 @@ func WithNamespaces(daemon *Daemon, c *container.Container) coci.SpecOpts {
 		}
 		switch {
 		case ipcMode.IsContainer():
-			ic, err := daemon.getIpcContainer(ipcMode.Container())
+			ic, err := daemon.getIPCContainer(ipcMode.Container())
 			if err != nil {
-				return errors.Wrapf(err, "invalid IPC mode: %v", ipcMode)
+				return errors.Wrap(err, "failed to join IPC namespace")
 			}
 			setNamespace(s, specs.LinuxNamespace{
 				Type: specs.IPCNamespace,
@@ -526,7 +526,7 @@ func withMounts(daemon *Daemon, daemonCfg *configStore, c *container.Container)
 			return err
 		}
 
-		if err := daemon.setupIpcDirs(c); err != nil {
+		if err := daemon.setupIPCDirs(c); err != nil {
 			return err
 		}