Implement host probing retry with major refactoring

- Implement probe retry
- Switch to typical core/provider design pattern for HostProbingService
  and as a result decoupling the dependency between SR and HostLocationProvider

Change-Id: I33a15af580677ea376b421ac3e26f9821dcca844
diff --git a/providers/pom.xml b/providers/pom.xml
index 36781ac..948c9e0 100644
--- a/providers/pom.xml
+++ b/providers/pom.xml
@@ -33,6 +33,7 @@
     <modules>
         <module>openflow</module>
         <module>host</module>
+        <module>hostprobing</module>
         <module>netcfghost</module>
         <module>netconf</module>
         <module>null</module>