Add basic vagrant compilation capability

Add 	FREECAD_USER_DATA environment variable required to support snap on ubuntu which is using Apparmor to
	limit application access to filesystem.
Add	automatic snap build on Xenial (ubuntu 16.04) within Vagrant build
Info	Build results are into /home/vagrant/Results (deb + snap

src/App/Application.cpp

@@ -1909,7 +1909,12 @@ void Application::ExtractUserPath()
     if (pwd == NULL)
         throw Base::Exception("Getting HOME path from system failed!");
     mConfig["UserHomePath"] = pwd->pw_dir;
-    std::string appData = pwd->pw_dir;
+    char *path="/tmp";
+    if ( FCUserData=getenv("FREECAD_USER_DATA") )
+        path=FCUserData;
+    else
+                path= pwd->pw_dir;
+    std::string appData(path);
     Base::FileInfo fi(appData.c_str());
     if (!fi.exists()) {
         // This should never ever happen