Find the path of the chef gem correctly while installing chef-client service via MSI.

Previously we have been using the DisplayVersionNumber of chef gem while installing chef-client as a service on windows. However this didn't work with non default versions such as 11.6.0.rc.0. 

This change searches for the chef gem under the installation directory and updates the start command of the service based on the found path. 

Change is run through CI and verified manually by installing the MSI and using chef-service-manager.