X test.go ↑ timeout 10m -> 20m

xbtree tests, in normal mode, run ~ 130s on my laptop. On a testnode
however they run ~500s and sometimes more than 10 minutes, probably
depending on surrounding load.

-> increase default `go test` timeout to avoid sporadic "test timed out"
failures.

Makefile

@@ -187,7 +187,9 @@ test.py.drd: bigfile/_bigfile.so wcfs/wcfs
 
 # run go tests
 test.go	:
-	cd wcfs && $(GO) test -count=1 ./... # -count=1 disables tests caching
+	cd wcfs && $(GO) test -timeout=20m -count=1 ./... # -count=1 disables tests caching
+	# -timeout=20m: xbtree tests are computationally expensive, and
+	# sometime cross 10 minutes border when testnodes are otherwise loaded.
 
 
 # test pagefault for double/real faults - it should crash