Fix find PerformanceCounterInstance

It does not always 'startswith' - running as application or debugging on my win81
pc the Instancename is:
'Raven.Server.vshost/1-UxBsU-C:\Users\SteinArild\Source\Repos\RavenDb\build\Database'
trying to match uniquePrefix = '1-UxBsU'
corrected spelling(utiliti => utility)
Merge branch 'RavenDB-1631' of github.com:ppekrol/ravendb
Merge branch 'master' of https://github.com/ghuntley/ravendb
Merge branch 'master' of github.com:ayende/ravendb