testing: fix shell command quoting to work the same on Unix and Windows (#1925)

Signed-off-by: Larry Gritz <[email protected]>

Author: lgritz

testsuite/lazytrace/run.py

@@ -12,4 +12,4 @@
 
 # Run once with default (lazytrace=1), and once explicitly disabled
 command += testshade(shader_commands)
-command += testshade("{} --options 'lazytrace=0'".format(shader_commands))
+command += testshade("{} --options \"lazytrace=0\"".format(shader_commands))

testsuite/reparam-string/run.py

@@ -6,9 +6,9 @@
 
 command += testshade(" ".join([
     "--layer lay0",
-    "--param:type=string:interactive=1 test_string 'initial value'",
+    "--param:type=string:interactive=1 test_string \"initial value\"",
     "test --iters 2",
-    "--reparam:type=string:interactive=1 lay0 test_string 'updated value'",
+    "--reparam:type=string:interactive=1 lay0 test_string \"updated value\"",
 ]))
 
 outputs = [ "out.txt" ]