target: Add Target.execute(force_locale='C') parameter

To avoid locale-specific variations in the output of commands, set LC_ALL=C by
default. This can be disabled by using None, or set to another locale.

devlib/target.py

@@ -385,10 +385,19 @@ class Target(object):
     # execution
 
     def execute(self, command, timeout=None, check_exit_code=True,
-                as_root=False, strip_colors=True, will_succeed=False):
+                as_root=False, strip_colors=True, will_succeed=False,
+                force_locale='C'):
+
+        # Force the locale if necessary for more predictable output
+        if force_locale:
+            # Use an explicit export so that the command is allowed to be any
+            # shell statement, rather than just a command invocation
+            command = 'export LC_ALL={} && {}'.format(quote(force_locale), command)
+
         # Ensure to use deployed command when availables
         if self.executables_directory:
             command = "PATH={}:$PATH && {}".format(self.executables_directory, command)
+
         return self.conn.execute(command, timeout=timeout,
                 check_exit_code=check_exit_code, as_root=as_root,
                 strip_colors=strip_colors, will_succeed=will_succeed)

doc/target.rst

@@ -232,7 +232,7 @@ Target
    :param timeout: timeout (in seconds) for the transfer; if the transfer does
        not  complete within this period, an exception will be raised.
 
-.. method:: Target.execute(command [, timeout [, check_exit_code [, as_root [, strip_colors [, will_succeed]]]]])
+.. method:: Target.execute(command [, timeout [, check_exit_code [, as_root [, strip_colors [, will_succeed [, force_locale]]]]]])
 
    Execute the specified command on the target device and return its output.
 
@@ -252,6 +252,9 @@ Target
        will make the method always raise an instance of a subclass of
        :class:`DevlibTransientError` when the command fails, instead of a
        :class:`DevlibStableError`.
+   :param force_locale: Prepend ``LC_ALL=<force_locale>`` in front of the
+      command to get predictable output that can be more safely parsed.
+      If ``None``, no locale is prepended.
 
 .. method:: Target.background(command [, stdout [, stderr [, as_root]]])