Move gio tests from gio/tests/ to tests/gio/

This avoids getting tests built every time when working on libgio and
running make in the gio/ directory.

gio/tests/.gitignore

@@ -1,24 +0,0 @@
-buffered-input-stream
-desktop-app-info
-g-icon
-simple-async-result
-unix-streams
-data-input-stream
-data-output-stream
-g-file
-g-file-info
-live-g-file
-memory-input-stream
-memory-output-stream
-filter-streams
-sleepy-stream
-resolver
-connectable
-echo-server
-httpd
-readwrite
-send-data
-socket-client
-socket-server
-srvtarget
-contexts