slapgrid: fix invocation of bootstrapBuildout

This commit reverts ddd77222.

The goal is to fix nexedi/slapos.buildout!25 (comment 148861)

os.environ is a special mapping object that transparently modifies the
actual environment and we should never make os.environ make point to
something else (see
nexedi/slapos.buildout!25 (comment 149333)
and https://docs.python.org/3/library/os.html#os.environ)

Instead change the environment only when calling SlapPopen. We will see
if the problems fixed by ddd77222 appear
again...

slapos/grid/SlapObject.py

@@ -266,9 +266,6 @@ class Software(object):
     """ Fetches buildout configuration from the server, run buildout with
     it. If it fails, we notify the server.
     """
-    root_stat = os.stat(self.software_root)
-    os.environ = getCleanEnvironment(logger=self.logger,
-                                     home_path=pwd.getpwuid(root_stat.st_uid).pw_dir)
     try:
       os.mkdir(self.software_path)
     except OSError as e:
@@ -604,8 +601,6 @@ class Partition(object):
                                  'permissions are: 0%o, wanted are 0%o' %
                                  (self.instance_path, permission,
                                   REQUIRED_COMPUTER_PARTITION_PERMISSION))
-    os.environ = getCleanEnvironment(logger=self.logger,
-                                     home_path=pwd.getpwuid(instance_stat_info.st_uid).pw_dir)
 
     # Check that Software Release directory is present
     if not os.path.exists(self.software_path):

slapos/grid/utils.py

@@ -341,6 +341,8 @@ def bootstrapBuildout(path, logger, buildout=None,
     process_handler = SlapPopen(invocation_list,
                                 preexec_fn=lambda: dropPrivileges(uid, gid, logger=logger),
                                 cwd=path,
+                                env=getCleanEnvironment(logger,
+                                     home_path=pwd.getpwuid(os.stat(path).st_uid).pw_dir),
                                 logger=logger)
     if process_handler.returncode is None or process_handler.returncode != 0:
       message = 'Failed to run buildout profile in directory %r' % path