test.bash: disable result caching

Go 1.10 has introduced test result caching and
enabled it by default.

This does not work properly for our integration
tests because they test the compiled binary and
do not have a source level dependency on the
gocryptfs code.

Disable caching.

test.bash

@@ -38,8 +38,12 @@ else
 	go tool vet -all -shadow .
 fi
 
-# We don't want all the subprocesses holding the lock file open
-go test ./... $* 200>&-
+#            We don't want all the subprocesses
+#               holding the lock file open
+#                         vvvvv
+go test -count 1 ./... $* 200>&-
+#       ^^^^^^^^
+#   Disable result caching
 
 # The tests cannot to this themselves as they are run in parallel.
 # Don't descend into possibly still mounted example filesystems.