fate.sh: Ignore errors from rm command during cleanup.

The install directory being deleted might not be present if the build failed.
This can lead to annoying error output if the FATE client is run as a cronjob.

tests/fate.sh

@@ -70,7 +70,7 @@ fate()(
 )
 
 clean(){
-    rm -r ${build} ${inst}
+    rm -rf ${build} ${inst}
 }
 
 report(){