Fix FUSE integration test failed with ECONNREFUSED
Fix FUSE integration test failed with ECONNREFUSED

The newer version of FUSE_INIT checks the response from the FUSE server
if its major number is equal to 7. If it's not, then FUSE_INIT fails and
further filesystem operations will get ECONNREFUSED. To mitigate this
issue, we can send back a response with major version equals to 7 when
consuming the first FUSE_INIT request.

Fixes #3500

google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor