Repair vsphere provider

This patch fixes up the vsphere provider to make it much more rebust and
capable of handling transient errors.

We have wrapped retry blocks around the API connection routines, the SSH
connection handling and the Node launching code.

Signed-off-by: Ken Barber <ken@bob.sh>
Merge pull request #59 from kbarber/vsphere-fixes

Repair vsphere provider
Release 2.5.0

Signed-off-by: Ken Barber <ken@bob.sh>
Merge branch 'release_250'

* release_250:
  Release 2.5.0
Fix hostname of box for vsphere

The VSphere provider doesn't set the hostname of a box automatically like
vagrant. This patch does the work automatically and includes a test to ensure
it worked.

It also updates /etc/hosts to remove any resolution errors.

Signed-off-by: Ken Barber <ken@bob.sh>
Merge pull request #64 from kbarber/vsphere-hostname

Fix hostname of box
Release 2.5.1

Release notes and gemspec changes for release 2.5.1.

Signed-off-by: Ken Barber <ken@bob.sh>