Restrict osc mpcdf_push to home:* -> software

Consequentially, the last arguments becomes deprecated, as it always
would be "software"

mpcdf_push.py

@@ -29,9 +29,9 @@ def do_mpcdf_push(self, subcmd, opts, *args):
     the osc mpcdf_set_as_branch command)
 
     Usage:
-        osc mpcdf_push TO_PROJECT           (from within a package checkout)
-        osc mpcdf_push PACKAGE TO_PROJECT   (from within a project checkout)
-        osc mpcdf_push FROM_PROJECT PACKAGE TO_PROJECT            (anywhere)
+        osc mpcdf_push ["software"]         (from within a package checkout)
+        osc mpcdf_push PACKAGE ["software"] (from within a project checkout)
+        osc mpcdf_push FROM_PROJECT PACKAGE ["software"]          (anywhere)
 
     Examples:
        - Add a new package from your home:project to software:
@@ -41,26 +41,34 @@ def do_mpcdf_push(self, subcmd, opts, *args):
     """
     import sys
 
-    if len(args) < 1:
-        raise osc.oscerr.WrongArgs("Not enough arguments")
-    elif len(args) == 1:
-        to_project, = args
+    if len(args) > 0 and args[-1] == "software":
+        print("Deprecation Notice:\n"
+              "  'osc mpcdf_push' can only be used to push to the 'software' project,\n"
+              "  it is thus no longer necessary as an argument\n")
+        args = args[:-1]
+
+    to_project = "software"
+
+    if len(args) == 0:
         if osc.core.is_package_dir(os.curdir):
             package = osc.core.store_read_package(os.curdir)
             from_project = osc.core.store_read_project(os.curdir)
         else:
             raise osc.oscerr.WrongArgs('Specify FROM_PROJECT and/or PACKAGE or run command in a package or project checkout directory')
-    elif len(args) == 2:
-        package, to_project = args
+    elif len(args) == 1:
+        package, = args
         if osc.core.is_project_dir(os.curdir):
             from_project = osc.core.store_read_project(os.curdir)
         else:
             raise osc.oscerr.WrongArgs('Specify FROM_PROJECT or run command in an osc package or project checkout directory')
-    elif len(args) == 3:
-        from_project, package, to_project = args
+    elif len(args) == 2:
+        from_project, package = args
     else:
         raise osc.oscerr.WrongArgs("Too many arguments")
 
+    if not from_project.startswith("home:"):
+        raise osc.oscerr.WrongArgs("'osc mpcdf_push' can only be used from packages in a home: project")
+
     api_url = self.get_api_url()
 
     project_attributes = ["MPCDF:compiler_modules", "MPCDF:cuda_modules", "MPCDF:mpi_modules"]