Add a pyplot based julia test case

tests/julia/pyplot/REQUIRE

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+PyPlot

tests/julia/pyplot/environment.yml

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+dependencies:
+  - matplotlib
+  

tests/julia/pyplot/verify

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+#!/usr/bin/env julia
+# We try to plot something, and see if the file saved exists
+using PyPlot
+x = linspace(0,2*pi,1000); y = sin(3*x + 4*cos(2*x))
+plot(x, y, color="red", linewidth=2.0, linestyle="--")
+savefig("graph.png")
+if isfile("graph.png")
+    exit(0)
+else
+    exit(1)
+end
+