Fix variable shadow warnings in sdbusplus

-Wshadow is useful for subprojects to enable, because it can find bugs
in common variable names (err, r, i, etc).  With these changes, projects
can now build sdbusplus with -Wshadow enabled.

The changes fall into a couple buckets.  The first is for constructor
variables that match the member variable name.  In these cases, "_in" is
appended to the end of the constructor variable name.

The second is a case where the variable "r" was used for return codes
twice.  One instance is changed to "ret".

With these changes, projects can compile with -Wshadow enabled without
warnings.

Change-Id: Ia33a6f8306473c616f6278bb848460167e5463ef
Signed-off-by: Ed Tanous <edtanous@google.com>
diff --git a/src/exception.cpp b/src/exception.cpp
index 804fab8..a7a3596 100644
--- a/src/exception.cpp
+++ b/src/exception.cpp
@@ -21,14 +21,16 @@
     return EIO;
 }
 
-SdBusError::SdBusError(int error, const char* prefix, SdBusInterface* intf) :
-    error(SD_BUS_ERROR_NULL), intf(intf)
+SdBusError::SdBusError(int error_in, const char* prefix,
+                       SdBusInterface* intf_in) :
+    error(SD_BUS_ERROR_NULL),
+    intf(intf_in)
 {
     // We can't check the output of intf->sd_bus_error_set_errno() because
     // it returns the input errorcode. We don't want to try and guess
     // possible error statuses. Instead, check to see if the error was
     // constructed to determine success.
-    intf->sd_bus_error_set_errno(&this->error, error);
+    intf->sd_bus_error_set_errno(&this->error, error_in);
     if (!intf->sd_bus_error_is_set(&this->error))
     {
         throw std::runtime_error("Failed to create SdBusError");
@@ -37,13 +39,13 @@
     populateMessage(prefix);
 }
 
-SdBusError::SdBusError(sd_bus_error* error, const char* prefix,
-                       SdBusInterface* intf) :
-    error(*error),
-    intf(intf)
+SdBusError::SdBusError(sd_bus_error* error_in, const char* prefix,
+                       SdBusInterface* intf_in) :
+    error(*error_in),
+    intf(intf_in)
 {
     // We own the error so remove the caller's reference
-    *error = SD_BUS_ERROR_NULL;
+    *error_in = SD_BUS_ERROR_NULL;
 
     populateMessage(prefix);
 }