[PATCH] gdbus tests: wait up to 60s for gdbus-testserver to take its bus name

Had to manually apply parts of the patch since it wouldn't do it cleanly

Original patch details below:

Previously, we waited up to 0.5s, but that can fail on slow
architectures like ARM; now we wait up to 60s in 0.1s increments.

Patch originally by Simon McVittie <simon.mcvittie@collabora.co.uk>,
modified by Iain Lane to be called earlier, to catch all testcases in a
particular test.

https://bugzilla.gnome.org/show_bug.cgi?id=724113