Add -D logdir option to Auster so that the whole logdir can be specified

Add -D logdir option to Auster so that the whole logdir can be specified

Added a -D logdir so that Auster does not append a time based suffix to the dir
this means that the location of the logs can be known by the parent of Auster

Use Case: The job manager needs to place console logs into the logs directory
and is a parent of Auster, therefor the job manage creates a directory and passes
it to auster using the -D option

Issue: LU-105
Change-Id: Idbd258677b9c6624fdac43aa6223fe6f516bc989
Signed-off-by: Chris Gearing <chris@whamcloud.com>