fix iodaemon race with quickly existing processes

previously the goroutine waiting for the process to exit could fire and
exit(0) before printing the 'pid:' line, which is used for synchronizing
the spawning and linking of the process.
link to processes in-process, rather than shelling out

Signed-off-by: Max Brunsfeld <mbrunsfeld@pivotallabs.com>
Merge branch 'inline-iodaemon-link'

Signed-off-by: Max Brunsfeld <mbrunsfeld@pivotallabs.com>

Conflicts:
	linux_backend/process_tracker/process_tracker_test.go