Task query optional parameters (#69)

* Change TaskQuery struct parameters to optional

* Thrift API is modified to make all the parameters in the
  TaskQuery struct optional

* Autogenerated code is regenerated

* Changes in TaskQuery structs used in the project

* Now that TaskQuery receive optional values, pointers
  instead of values must be passed to the struct

auroraAPI.thrift

@@ -540,16 +540,16 @@ struct GetJobsResult {
  * (terms are AND'ed together).
  */
 struct TaskQuery {
-  14: string role
-  9: string environment
-  2: string jobName
-  4: set<string> taskIds
-  5: set<ScheduleStatus> statuses
-  7: set<i32> instanceIds
-  10: set<string> slaveHosts
-  11: set<JobKey> jobKeys
-  12: i32 offset
-  13: i32 limit
+  14: optional string role
+  9: optional string environment
+  2: optional string jobName
+  4: optional set<string> taskIds
+  5: optional set<ScheduleStatus> statuses
+  7: optional set<i32> instanceIds
+  10: optional set<string> slaveHosts
+  11: optional set<JobKey> jobKeys
+  12: optional i32 offset
+  13: optional i32 limit
 }
 
 struct HostStatus {