Revert "Revert "/bin/wifi:  Lock /bin/wifi to prevent simultaneous calls.""

This reverts commit 6ccdd2cd8c62651ed31f2ed8e11ec107b1a0ded3.

This has been substantially rewritten, since fcntl.lockf failed about
5% of the time for no apprent reason.  The main change is that this
now uses subprocess calls to lockfile-create.  This required rewriting
the timing, the tests, etc.

Change-Id: Ic1b4152dd13a9fca72a19900b610ef82cfd546b3
3 files changed