Add shared helper method to detect if running version is prerelease

lib/vagrant/shared_helpers.rb

@@ -102,4 +102,12 @@ module Vagrant
 
     Pathname.new(path).expand_path
   end
+
+  # This returns true/false if the running version of Vagrant is
+  # a pre-release version (development)
+  #
+  # @return [Boolean]
+  def self.prerelease?
+    Gem::Version.new(Vagrant::VERSION).prerelease?
+  end
 end

test/unit/vagrant/shared_helpers_test.rb

@@ -131,4 +131,16 @@ describe Vagrant do
       end
     end
   end
+
+  describe "#prerelease?" do
+    it "should return true when Vagrant version is development" do
+      stub_const("Vagrant::VERSION", "1.0.0.dev")
+      expect(subject.prerelease?).to be(true)
+    end
+
+    it "should return false when Vagrant version is release" do
+      stub_const("Vagrant::VERSION", "1.0.0")
+      expect(subject.prerelease?).to be(false)
+    end
+  end
 end