DodoApp: Support volume requests

Users can define volumes section under app, and for each volume
corresponding env variable will be passed down to the application.

Change-Id: I8da9d5e1ca652cdb2f0196fcba1b6242064d057f
diff --git a/apps/app-runner/server.go b/apps/app-runner/server.go
index 665f493..865f724 100644
--- a/apps/app-runner/server.go
+++ b/apps/app-runner/server.go
@@ -98,6 +98,7 @@
 			Dir:    *appDir,
 			Path:   c.Bin,
 			Args:   args,
+			Env:    c.Env,
 			Stdout: os.Stdout,
 			Stderr: os.Stderr,
 		}