More error information is needed wrt. remote files (iterative#1737)

As described in iterative#1735, I think DVC needs to output more info about remote files,
Thus, I have added this to stage.py.
Additionally, I think that DVC should not crash if the SSH client is trying to remove a fil which already does not exists. This, I have implemented the catch of the FileNotFoundError : [Errno 2] No such file exception.

Fixes iterative#1735

.gitignore

@@ -27,3 +27,6 @@ innosetup/config.ini
 dvc/version.py
 
 *.swp
+
+pip-wheel-metadata/
+.vscode/

dvc/remote/ssh/connection.py

@@ -1,3 +1,4 @@
+import errno
 import os
 import posixpath
 
@@ -143,7 +144,11 @@ def walk_files(self, directory):
 
     def remove(self, path):
         self._sftp_connect()
-        self._sftp.remove(path)
+        try:
+            self._sftp.remove(path)
+        except IOError as exc:
+            if exc.errno != errno.ENOENT:
+                raise
 
     def download(self, src, dest, no_progress_bar=False, progress_title=None):
         self._sftp_connect()

dvc/stage.py

@@ -211,10 +211,12 @@ def _changed_deps(self):
             return True
 
         for dep in self.deps:
-            if dep.changed():
+            status = dep.status()
+            if status:
                 logger.warning(
-                    "Dependency '{dep}' of '{stage}' changed.".format(
-                        dep=dep, stage=self.relpath
+                    "Dependency '{dep}' of '{stage}' changed because it is "
+                    "'{status}'.".format(
+                        dep=dep, stage=self.relpath, status=status[str(dep)]
                     )
                 )
                 return True
@@ -223,10 +225,12 @@ def _changed_deps(self):
 
     def _changed_outs(self):
         for out in self.outs:
-            if out.changed():
+            status = out.status()
+            if status:
                 logger.warning(
-                    "Output '{out}' of '{stage}' changed.".format(
-                        out=out, stage=self.relpath
+                    "Output '{out}' of '{stage}' changed because it is "
+                    "'{status}'".format(
+                        out=out, stage=self.relpath, status=status[str(out)]
                     )
                 )
                 return True
@@ -256,10 +260,13 @@ def changed(self):
         return ret
 
     def remove_outs(self, ignore_remove=False):
-        """
-        Used mainly for `dvc remove --outs`
-        """
+        """Used mainly for `dvc remove --outs` and :func:`Stage.reproduce`."""
         for out in self.outs:
+            logger.debug(
+                "Removing output '{out}' of '{stage}'.".format(
+                    out=out, stage=self.relpath
+                )
+            )
             out.remove(ignore_remove=ignore_remove)
 
     def unprotect_outs(self):