lockfile: Don't warn if successful lock takes a little time.

lockfile: Don't warn if successful lock takes a little time.

This code issues a warning if obtaining a lock takes even 1 millisecond.
That's far too aggressive.  There's no need to warn if we have to wait
a few milliseconds.  This function already warns elsewhere if locking takes
more than 1 second, which is much more reasonable.

This change allows us to test ovsdb-server stderr output more carefully.
Before now, the tests had to ignore what ovsdb-server writes to stderr
because sometimes it would log a warning that locking took 1 ms (or so).

Reviewed-by: Simon Horman <horms@verge.net.au>