Add configurable VM tries to director.yml config

Signed-off-by: Mike Stallard <mstallard@pivotallabs.com>
Move max_create_vm_tries into director properties

Signed-off-by: Mike Stallard <mstallard@pivotallabs.com>
Disambiguates BATs artifacts dir so jobs can run in parallel

Signed-off-by: Mike Stallard <mstallard@pivotallabs.com>