Extend task_fetch retries

More beaker jobs are now relying on fetching tasks from git repos, and intermitted connectivity issue are causing unnecessary problems when restraint only tries a couple of times in half a minute.
It's a much bigger issue when core tasks like kernelinstall was aborted for that reason. The remaining tests in the recipe become pointless and even misleading due to false positive/negative from wrong kernel.
This minor change is increasing the number and interval of task_fetch retries - to make future jobs more tolerant with intermitted connectivity issue.

src/task.h

@@ -41,8 +41,8 @@
 #define ROLE_REFRESH_INTERVAL 10
 #define ROLE_REFRESH_RETRIES 3
 
-#define TASK_FETCH_INTERVAL 10
-#define TASK_FETCH_RETRIES 3
+#define TASK_FETCH_INTERVAL 20
+#define TASK_FETCH_RETRIES 30
 
 typedef enum {
     TASK_IDLE,