Fix powershell execution problems
Fix powershell execution problems

'powershell' and '-Command' need to be passed as discrete arguments

[#177187969](https://www.pivotaltracker.com/story/show/177187969)

Signed-off-by: Brian Upton <633483f7295e665b4a23d10cfc31c2458b36dfcc@vmware.com>

cloudfoundry/bosh-agent,cloudfoundry/bosh-agent