Changes

zfs: fix incorrect permissions (staticcheck)
``` 13:06:14 daemon/graphdriver/zfs/zfs.go:57:50: SA9002: file mode
'600' evaluates to 01130; did you mean '0600'? (staticcheck) 13:06:14 
file, err := os.OpenFile("/dev/zfs", os.O_RDWR, 600)
```
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

daemon: Remove btrfs_noversion build flag
btrfs_noversion was added in d7c37b5a28de6e7c0a9270815c092a45d8d7fef7 
for distributions that did not have the `btrfs/version.h` header file.
Seeing how all of the distributions we currently support do have the
`btrfs/version.h` file we should probably just remove this build flag 
altogether.
Signed-off-by: Eli Uriegas <eli.uriegas@docker.com>

Improve integration test detecetor
The "new test" detector in test-integration-flaky was a bit flaky since 
it would detect function signatures that are not new tests.
In addition, the test calls `return` outside of a function which is not 
allowed.
Signed-off-by: Brian Goff <cpuguy83@gmail.com>