Added support for PS Core to fix #11085powershell-fix

Added an additional path check for "pwsh" to detect versionf of PowerShell Core that may be on the user's PATH. This also opens up the possibility of removing Windows specific references in this file, as Core can be installed on Linux and mac OS, giving us the ability to expand Powershell into a cross-platform plugin.

Signed-off-by: Scott Simontis <yo@scottsimontis.io>

lib/vagrant/util/powershell.rb

@@ -15,6 +15,7 @@ module Vagrant
       # Number of seconds to wait while attempting to get powershell version
       DEFAULT_VERSION_DETECTION_TIMEOUT = 30
       LOGGER = Log4r::Logger.new("vagrant::util::powershell")
+      POWERSHELL_CORE_EXE = "pwsh"
 
       # @return [String|nil] a powershell executable, depending on environment
       def self.executable
@@ -34,6 +35,8 @@ module Vagrant
                   @_powershell_executable = nil
                 end
               end
+            elsif !Which.which(POWERSHELL_CORE_EXE).nil?
+              @_powershell_executable = POWERSHELL_CORE_EXE
             else
               @_powershell_executable = nil
             end