Properly handle OCI runtime being set to a path

This is done by the --runtime flag, and as such, by all our CI.

Signed-off-by: Matthew Heon <matthew.heon@pm.me>

libpod/runtime.go

@@ -6,6 +6,7 @@ import (
 	"io/ioutil"
 	"os"
 	"path/filepath"
+	"strings"
 	"sync"
 	"syscall"
 
@@ -837,14 +838,36 @@ func makeRuntime(ctx context.Context, runtime *Runtime) (err error) {
 		runtime.ociRuntimes[name] = ociRuntime
 	}
 
-	// Set default runtime
+	// Do we have a default OCI runtime?
 	if runtime.config.OCIRuntime != "" {
+		// If the string starts with / it's a path to a runtime
+		// executable.
+		if strings.HasPrefix(runtime.config.OCIRuntime, "/") {
+			name := filepath.Base(runtime.config.OCIRuntime)
+
+			supportsJSON := false
+			for _, r := range runtime.config.RuntimeSupportsJSON {
+				if r == name {
+					supportsJSON = true
+					break
+				}
+			}
+
+			ociRuntime, err := newOCIRuntime(name, []string{runtime.config.OCIRuntime}, runtime.conmonPath, runtime.config, supportsJSON)
+			if err != nil {
+				return err
+			}
+
+			runtime.ociRuntimes[name] = ociRuntime
+			runtime.defaultOCIRuntime = ociRuntime
+		} else {
 			ociRuntime, ok := runtime.ociRuntimes[runtime.config.OCIRuntime]
 			if !ok {
 				return errors.Wrapf(ErrInvalidArg, "default OCI runtime %q not found", runtime.config.OCIRuntime)
 			}
 			runtime.defaultOCIRuntime = ociRuntime
 		}
+	}
 
 	// Do we have at least one valid OCI runtime?
 	if len(runtime.ociRuntimes) == 0 {