DrawLines_PointFs, DrawBezier_PointFs, DrawBezier_Points and DrawLines_Points failing sporadically in CI

I've seen these fail multiple times in CI now, e.g.
https://mc.dot.net/#/user/dotnet-maestro-bot/pr~2Fjenkins~2Fdotnet~2Fcorefx~2Fmaster~2F/test~2Ffunctional~2Fcli~2F/7868028f16d0fb97037930838ec20cba5077191f/workItem/System.Drawing.Common.Tests/wilogs
```
2018-06-26 22:47:39,723: INFO: proc(54): run_and_log_output: Output: System.Drawing.Tests.Graphics_DrawBezierTests.DrawBezier_PointFs [FAIL]
2018-06-26 22:47:39,723: INFO: proc(54): run_and_log_output: Output: Assert.Equal() Failure
2018-06-26 22:47:39,723: INFO: proc(54): run_and_log_output: Output: Expected: Byte[] [208, 0, 8, 33, 6, ...]
2018-06-26 22:47:39,723: INFO: proc(54): run_and_log_output: Output: Actual: Byte[] [27, 206, 219, 21, 255, ...]
2018-06-26 22:47:39,737: INFO: proc(54): run_and_log_output: Output: Stack Trace:
2018-06-26 22:47:39,987: INFO: proc(54): run_and_log_output: Output: D:\j\workspace\windows-TGrou---f8ac6754\src\System.Drawing.Common\tests\DrawingTest.cs(21,0): at System.Drawing.Tests.DrawingTest.ValidateImageContent(Image image, Byte[] expectedHash)
2018-06-26 22:47:39,987: INFO: proc(54): run_and_log_output: Output: D:\j\workspace\windows-TGrou---f8ac6754\src\System.Drawing.Common\tests\Graphics_DrawBezierTests.cs(59,0): at System.Drawing.Tests.Graphics_DrawBezierTests.DrawBezier_PointFs()
2018-06-26 22:47:39,987: INFO: proc(54): run_and_log_output: Output: System.Drawing.Tests.Graphics_DrawLineTests.DrawLines_PointFs [FAIL]
2018-06-26 22:47:39,987: INFO: proc(54): run_and_log_output: Output: Assert.Equal() Failure
2018-06-26 22:47:39,987: INFO: proc(54): run_and_log_output: Output: Expected: Byte[] [142, 194, 251, 180, 222, ...]
2018-06-26 22:47:39,987: INFO: proc(54): run_and_log_output: Output: Actual: Byte[] [89, 188, 96, 22, 200, ...]
2018-06-26 22:47:39,987: INFO: proc(54): run_and_log_output: Output: Stack Trace:
2018-06-26 22:47:39,987: INFO: proc(54): run_and_log_output: Output: D:\j\workspace\windows-TGrou---f8ac6754\src\System.Drawing.Common\tests\DrawingTest.cs(21,0): at System.Drawing.Tests.DrawingTest.ValidateImageContent(Image image, Byte[] expectedHash)
2018-06-26 22:47:39,987: INFO: proc(54): run_and_log_output: Output: D:\j\workspace\windows-TGrou---f8ac6754\src\System.Drawing.Common\tests\Graphics_DrawLineTests.cs(32,0): at System.Drawing.Tests.Graphics_DrawLineTests.DrawLines_PointFs()
```
I could be wrong, but I believe I only started seeing it after https://github.com/dotnet/corefx/pull/30099.
cc: @safern, @JeremyKuhne