Force usage of pip < 8 version

We need to fix this in 2 places:

- install_rally.sh
- rally verify tempest installation

In case of Tempest we should not use unclear non-working scripts
from tempest/tools to create env

Closes-bug: #1536436
Change-Id: I72d581d07fa9df231517ecca762525e7f28d12bb

install_rally.sh

@@ -348,7 +348,7 @@ __EOF__
                         if ask_yn "Error installing python-pip. Install from external source?"; then
                             local pdir=$(mktemp -d)
                             local getpip="$pdir/get-pip.py"
-                            download "$getpip" https://raw.github.com/pypa/pip/master/contrib/get-pip.py
+                            download "$getpip" https://bootstrap.pypa.io/get-pip.py
                             if ! "$PYTHON" "$getpip"; then
                                 abort $EX_PROTOCOL "Error while installing python-pip from external source."
                             fi
@@ -737,7 +737,7 @@ install_db_connector
 # Install rally
 cd "$SOURCEDIR"
 # Get latest available pip and reset shell cache
-pip install -i $BASE_PIP_URL -U 'pip'
+pip install -i $BASE_PIP_URL -U 'pip<8'
 hash -r
 
 # Install dependencies

rally/verification/tempest/tempest.py

@@ -197,7 +197,7 @@ class Tempest(object):
             else:
                 python_interpreter = sys.executable
             try:
-                check_output([python_interpreter, "./tools/install_venv.py"],
+                check_output(["virtualenv", "-p", python_interpreter, ".venv"],
                              cwd=self.path())
                 # NOTE(kun): Using develop mode installation is for run
                 #            multiple tempest instance. However, dependency

tests/unit/verification/test_tempest.py

@@ -108,7 +108,8 @@ class TempestUtilsTestCase(BaseTestCase):
 
         mock_isdir.assert_called_once_with(self.verifier.path(".venv"))
         mock_check_output.assert_has_calls([
-            mock.call(["python", "./tools/install_venv.py"], cwd="/tmp"),
+            mock.call(["virtualenv", "-p", mock_get_interpreter.return_value,
+                       ".venv"], cwd="/tmp"),
             mock.call(["/tmp/tools/with_venv.sh", "pip", "install", "-r",
                        "requirements.txt", "-r", "test-requirements.txt"],
                       cwd="/tmp"),