Add mock speedtest constructor

[maplant]

Add a mock speedtest constructor. This is so that the mobile rewards estimator can easily construct a collection of speedtests that are guaranteed to be assigned SpeedtestTier::Good when averaged.

I'm open to better ways of doing this, this just seemed like the easiest way

[michaeldjeffrey]

My alternative to creating speedtests was this.

oracles/coverage_point_calculator/tests/coverage_point_calculator.rs

Lines 406 to 431 in aecb7bc

	fn speedtests(tier: SpeedtestTier) -> Vec<Speedtest> {
	// SpeedtestTier is determined solely by upload_speed.
	// Other values are far surpassing ::Good.
	let upload_speed = BytesPs::mbps(match tier {
	SpeedtestTier::Good => 10,
	SpeedtestTier::Acceptable => 8,
	SpeedtestTier::Degraded => 5,
	SpeedtestTier::Poor => 2,
	SpeedtestTier::Fail => 0,
	});
	vec![
	Speedtest {
	upload_speed,
	download_speed: BytesPs::mbps(150),
	latency_millis: 0,
	timestamp: Utc::now(),
	},
	Speedtest {
	upload_speed,
	download_speed: BytesPs::mbps(150),
	latency_millis: 0,
	timestamp: Utc::now(),
	},
	]
	}