Fix gcloud can't run on python2 during acloud setup.

- Check gcloud alpha component uninstall before intall it.
- Change gcloud running environment to support python2.

Bug: 148623409
Test: acloud-dev setup --gcp-init --force
Change-Id: Idab3c03a256a6605f4620edde915b327d082d174
diff --git a/setup/gcp_setup_runner.py b/setup/gcp_setup_runner.py
index 14619c4..2d12ccc 100644
--- a/setup/gcp_setup_runner.py
+++ b/setup/gcp_setup_runner.py
@@ -55,6 +55,7 @@
                                         _DEFAULT_SSH_KEY)
 _DEFAULT_SSH_PUBLIC_KEY = os.path.join(_DEFAULT_SSH_FOLDER,
                                        _DEFAULT_SSH_KEY + ".pub")
+_ENV_CLOUDSDK_PYTHON = "CLOUDSDK_PYTHON"
 _GCLOUD_COMPONENT_ALPHA = "alpha"
 # Regular expression to get project/zone information.
 _PROJECT_RE = re.compile(r"^project = (?P<project>.+)")
@@ -150,6 +151,9 @@
         """
         self.gcloud_command_path = os.path.join(google_sdk_folder, "gcloud")
         self.gsutil_command_path = os.path.join(google_sdk_folder, "gsutil")
+        # TODO(137195528): Remove python2 environment after acloud support python3.
+        self._env = os.environ.copy()
+        self._env[_ENV_CLOUDSDK_PYTHON] = "python2"
 
     def RunGcloud(self, cmd, **kwargs):
         """Run gcloud command.
@@ -162,7 +166,8 @@
         Returns:
             String, return message after execute gcloud command.
         """
-        return subprocess.check_output([self.gcloud_command_path] + cmd, **kwargs)
+        return subprocess.check_output([self.gcloud_command_path] + cmd,
+                                       env=self._env, **kwargs)
 
     def RunGsutil(self, cmd, **kwargs):
         """Run gsutil command.
@@ -175,7 +180,8 @@
         Returns:
             String, return message after execute gsutil command.
         """
-        return subprocess.check_output([self.gsutil_command_path] + cmd, **kwargs)
+        return subprocess.check_output([self.gsutil_command_path] + cmd,
+                                       env=self._env, **kwargs)
 
 
 class GoogleAPIService(object):