accept() creates a new file descriptor that should be closed on exec so
that forked processes don't keep a fd opened on the socket.
This also fixes b/3297070 where adb hangs after running adb on the
target.
Change-Id: I8df511289e5549ae49b4824c9dfb71a3bf85eae8
Also check that device is not already connected in "adb connect"
Change-Id: I5f84b56b63d8c6932f23791cac319fd6bc39d36c
Signed-off-by: Mike Lockwood <lockwood@android.com>