Allow passing environent variables to StreamProcessors

Add support for an 'env' field to the StreamProcessor configuration
and append the environment variables found there to the os.Environ()
array.
The env field takes environment variables in the form of key=value.

Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>

services/server/config/config.go

@@ -80,6 +80,8 @@ type StreamProcessor struct {
 	Path string `toml:"path"`
 	// Args to the binary
 	Args []string `toml:"args"`
+	// Environment variables for the binary
+	Env []string `toml:"env"`
 }
 
 // GetVersion returns the config file's version