get-pipsi.py will now use the virtualenv installed in the python inte…

…rpreter

Instead of searching for the virtualenv command, use the virtualenv that
is installed in the python interpreter that is running
``python get-pipsi.py``. This will also fallback to using the ``venv``
package on python3. It's assumed if someone installed ``virtualenv``
then that overrides the default ``venv`` from the stdlib.

get-pipsi.py

@@ -16,6 +16,18 @@
     PIP = '/Scripts/pip.exe'
     PIPSI = '/Scripts/pipsi.exe'
 
+try:
+    import virtualenv
+    venv_pkg = 'virtualenv'
+    del virtualenv
+except ImportError:
+    try:
+        import venv
+        venv_pkg = 'venv'
+        del venv
+    except ImportError:
+        venv_pkg = None
+
 DEFAULT_PIPSI_HOME = os.path.expanduser('~/.local/venvs')
 DEFAULT_PIPSI_BIN_DIR = os.path.expanduser('~/.local/bin')
 
@@ -67,7 +79,7 @@ def _cleanup():
         except (OSError, IOError):
             pass
 
-    if call(['virtualenv', venv]) != 0:
+    if call([sys.executable, '-m', venv_pkg, venv]) != 0:
         _cleanup()
         fail('Could not create virtualenv for pipsi :(')
 
@@ -84,10 +96,9 @@ def main():
     else:
         echo('Installing pipsi')
 
-    if not command_exists('virtualenv'):
+    if venv_pkg is None:
         fail('You need to have virtualenv installed to bootstrap pipsi.')
 
-
     bin_dir = os.environ.get('PIPSI_BIN_DIR', DEFAULT_PIPSI_BIN_DIR)
     venv = os.path.join(os.environ.get('PIPSI_HOME', DEFAULT_PIPSI_HOME),
                         'pipsi')