Sync fs and move image deletion after loop detach

The warden tests frequently fail under VMware due to an error detatching
a loop device that was associated with a mounted disk image:

  loop: can't delete device /dev/loop0: Device or resource busy

In order to reduce the likelihood of the problem, a `sync` was added
before the detach and the deletion of the image file was moved until
after the detach.  After repeated runs with these modifications, I have
not seen the failures occur.
Don't rsync .vagrant into the VM

The rsync script does not exclude .vagrant when populating the test VM
with the code so if you happened to `vagrant up` the warden test VM from
the warden directory, you get your virtual machine copied into your
other virtual machine.

This simply excludes .vagrant from the sync.
Merge pull request #59 from sykesm/flakey-loopback-device

Sync fs and move image deletion after loop detach
Merge pull request #60 from sykesm/dont-rsync-vagrant

Don't rsync .vagrant into the VM
Create /dev/shm to allow python multiprocessing (esp for node)

[delivers #69306152]
Update readme

Signed-off-by: Chris Adams <cadams@pivotallabs.com>