when invalid depfile is specified, it is not handled gracefully

[rmm-fcul]

neither the --dry-run nor the actual experimental mode handle the absence of depfile cleanly.

--dry-run:
#[F] 11:37:13 > [F] assisi project file does not exist!: .assisi
Traceback (most recent call last):
exec_sim_timed.py", line 192, in init
self.validate_depfile(True)
line 579, in validate_depfile
if self.depfile is None:

AttributeError: 'SimHandler' object has no attribute 'depfile'

standard:

Traceback (most recent call last):
exec_sim_timed.py", line 382, in _arch_depconf
with open(pf) as project_file:
IOError: [Errno 2] No such file or directory: '/home/rmm/repos/bb/simln_ap/speeds/dep_speeds/all_links_twopair.assisi'