plugin mr mercurial, tools(common/utils): moved command protocol to a new module

sat/core/exceptions.py

@@ -126,3 +126,15 @@ class NotReady(Exception):
 class InvalidCertificate(Exception):
     """A TLS certificate is not valid"""
     pass
+
+
+class CommandException(RuntimeError):
+    """An external command failed
+
+    stdout and stderr will be attached to the Exception
+    """
+
+    def __init__(self, msg, stdout, stderr):
+        super(CommandException, self).__init__(msg)
+        self.stdout = stdout
+        self.stderr = stderr