add pytests for 'gpt rename' and 'gpt swap'

Add unit tests for the 'gpt rename' and 'gpt swap' commands that
rely on the block device created by test/py/make_test_disk.py.
Add CONFIG_CMD_GPT_RENAME to the sandbox_defconfig.  Remove the
testdisk.raw test device at the end of the tests.

Signed-off-by: Alison Chaiken <alison@peloton-tech.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/sandbox_defconfig b/configs/sandbox_defconfig
index 4c4e480..e7a61bd 100644
--- a/configs/sandbox_defconfig
+++ b/configs/sandbox_defconfig
@@ -34,6 +34,7 @@
 CONFIG_CMD_DEMO=y
 CONFIG_CMD_GPIO=y
 CONFIG_CMD_GPT=y
+CONFIG_CMD_GPT_RENAME=y
 CONFIG_CMD_IDE=y
 CONFIG_CMD_I2C=y
 CONFIG_CMD_PCI=y