tests: Return skip error if import fails

Rather than backtracing, just print the exception and return a skip
error if the import fails.

tests/virtual-image.py

@@ -1,6 +1,7 @@
 #!/usr/bin/env python3
 
-
+import sys
+try:
     import gi
     gi.require_version('FPrint', '2.0')
     from gi.repository import FPrint, GLib, Gio
@@ -15,6 +16,9 @@ import shutil
     import glob
     import cairo
     import tempfile
+except Exception as e:
+    print("Missing dependencies: %s" % str(e))
+    sys.exit(77)
 
 # Re-run the test with the passed wrapper if set
 wrapper = os.getenv('LIBFPRINT_TEST_WRAPPER')