test/py: use " for docstrings

Python's coding style docs indicate to use " not ' for docstrings.

test/py has other violations of the coding style docs, since the docs
specify a stranger style than I would expect, but nobody has complained
about those yet:-)

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/test/py/tests/test_shell_basics.py b/test/py/tests/test_shell_basics.py
index 719ce61..32e5f83 100644
--- a/test/py/tests/test_shell_basics.py
+++ b/test/py/tests/test_shell_basics.py
@@ -5,13 +5,13 @@
 # Test basic shell functionality, such as commands separate by semi-colons.
 
 def test_shell_execute(u_boot_console):
-    '''Test any shell command.'''
+    """Test any shell command."""
 
     response = u_boot_console.run_command('echo hello')
     assert response.strip() == 'hello'
 
 def test_shell_semicolon_two(u_boot_console):
-    '''Test two shell commands separate by a semi-colon.'''
+    """Test two shell commands separate by a semi-colon."""
 
     cmd = 'echo hello; echo world'
     response = u_boot_console.run_command(cmd)
@@ -19,8 +19,8 @@
     assert response.index('hello') < response.index('world')
 
 def test_shell_semicolon_three(u_boot_console):
-    '''Test three shell commands separate by a semi-colon, with variable
-    expansion dependencies between them.'''
+    """Test three shell commands separate by a semi-colon, with variable
+    expansion dependencies between them."""
 
     cmd = 'setenv list 1; setenv list ${list}2; setenv list ${list}3; ' + \
         'echo ${list}'
@@ -29,7 +29,7 @@
     u_boot_console.run_command('setenv list')
 
 def test_shell_run(u_boot_console):
-    '''Test the "run" shell command.'''
+    """Test the "run" shell command."""
 
     u_boot_console.run_command('setenv foo \"setenv monty 1; setenv python 2\"')
     u_boot_console.run_command('run foo')