PBR package testing improvements

We simplify virtualenv setup for PBR package installation testing by
switching to a simple file path for the PBR installation rather than a
full url with egg specifier. The egg specifer isn't necessary and
neither is the url and simpler is easier to understand.

We also add the verbose flag to the pip installations of tools into that
virtualenv to better understand problems when they occur.

Finally we add the option to skip writing package files if their
contents are empty. This allows us to ensure that we can omit certain
files which will be useful for the next change.

Change-Id: I1f081d29d62c905c1bb1abee5402b0990c83e948

pbr/tests/test_packaging.py

@@ -172,11 +172,10 @@ class Venv(fixtures.Fixture):
         """
         self._reason = reason
         if modules == ():
-            pbr = 'file://%s#egg=pbr' % PBR_ROOT
-            modules = ['pip', 'wheel', pbr]
+            modules = ['pip', 'wheel', PBR_ROOT]
         self.modules = modules
         if pip_cmd is None:
-            self.pip_cmd = ['-m', 'pip', 'install']
+            self.pip_cmd = ['-m', 'pip', '-v', 'install']
         else:
             self.pip_cmd = pip_cmd
 
@@ -230,6 +229,9 @@ class CreatePackages(fixtures.Fixture):
         self.packages = packages
 
     def _writeFile(self, directory, file_name, contents):
+        if not contents:
+            # We want to be able to override not having files
+            return
         path = os.path.abspath(os.path.join(directory, file_name))
         path_dir = os.path.dirname(path)
         if not os.path.exists(path_dir):