Utils: Replace Environment.isValid() with .hasChanges()

That's closer to the intended semantics. The "other" use in docker
will be changed to an optional<Environment> as follow-up to
keep this here mechanical.

Change-Id: I43ef9da6c9c7731b28f9d6fab6413ce9c4f428b4
Reviewed-by: Christian Kandeler <christian.kandeler@qt.io>

src/plugins/docker/dockerdevice.cpp

@@ -1137,10 +1137,10 @@ bool DockerDevicePrivate::addTemporaryMount(const FilePath &path, const FilePath
 
 Environment DockerDevicePrivate::environment()
 {
-    if (!m_cachedEnviroment.isValid())
+    if (!m_cachedEnviroment.hasChanges())
         fetchSystemEnviroment();
 
-    QTC_CHECK(m_cachedEnviroment.isValid());
+    QTC_CHECK(m_cachedEnviroment.hasChanges());
     return m_cachedEnviroment;
 }