tests: gpt: Remove test order dependency

Re-create a clean disk image for each test to prevent modifications from
one test affecting another

Signed-off-by: Joshua Watt <JPEWhacker@gmail.com>
diff --git a/test/py/tests/test_gpt.py b/test/py/tests/test_gpt.py
index 73bfbf7..339468b 100644
--- a/test/py/tests/test_gpt.py
+++ b/test/py/tests/test_gpt.py
@@ -61,18 +61,14 @@
         cmd = ('cp', persistent, self.path)
         u_boot_utils.run_and_log(u_boot_console, cmd)
 
-gtdi = None
 @pytest.fixture(scope='function')
 def state_disk_image(u_boot_console):
     """pytest fixture to provide a GptTestDiskImage object to tests.
     This is function-scoped because it uses u_boot_console, which is also
-    function-scoped. However, we don't need to actually do any function-scope
-    work, so this simply returns the same object over and over each time."""
+    function-scoped. A new disk is returned each time to prevent tests from
+    interfering with each other."""
 
-    global gtdi
-    if not gtdi:
-        gtdi = GptTestDiskImage(u_boot_console)
-    return gtdi
+    return GptTestDiskImage(u_boot_console)
 
 @pytest.mark.boardspec('sandbox')
 @pytest.mark.buildconfigspec('cmd_gpt')
@@ -186,12 +182,12 @@
 
     u_boot_console.run_command('host bind 0 ' + state_disk_image.path)
     output = u_boot_console.run_command('part list host 0')
-    assert '0x00000800	0x00000fff	"first"' in output
-    assert '0x00001000	0x00001bff	"second"' in output
-    u_boot_console.run_command('gpt swap host 0 first second')
+    assert '0x00000800	0x00000fff	"part1"' in output
+    assert '0x00001000	0x00001bff	"part2"' in output
+    u_boot_console.run_command('gpt swap host 0 part1 part2')
     output = u_boot_console.run_command('part list host 0')
-    assert '0x00000800	0x00000fff	"second"' in output
-    assert '0x00001000	0x00001bff	"first"' in output
+    assert '0x00000800	0x00000fff	"part2"' in output
+    assert '0x00001000	0x00001bff	"part1"' in output
 
 @pytest.mark.boardspec('sandbox')
 @pytest.mark.buildconfigspec('cmd_gpt')