Fix os.getlogin() problem with no tty

Catch OSError(s) from  os.getlogin() and fall back to looking at
environment variables to figure out the user's name. The OSError
is thrown where there is no tty for the python process when
os.getlogin() is called.

Related-Bug: #1221491

Change-Id: I2bd735c9669ba9d25da108da44ea602f358b2dcc

bin/cinder-rootwrap

@@ -62,6 +62,15 @@ def _exit_error(execname, message, errorcode, log=True):
     sys.exit(errorcode)
 
 
+def _getlogin():
+    try:
+        return os.getlogin()
+    except OSError:
+        return (os.getenv('USER') or
+                os.getenv('USERNAME') or
+                os.getenv('LOGNAME'))
+
+
 if __name__ == '__main__':
     # Split arguments, require at least a command
     execname = sys.argv.pop(0)
@@ -107,7 +116,7 @@ if __name__ == '__main__':
                                               exec_dirs=config.exec_dirs)
             if config.use_syslog:
                 logging.info("(%s > %s) Executing %s (filter match = %s)" % (
-                    os.getlogin(), pwd.getpwuid(os.getuid())[0],
+                    _getlogin(), pwd.getpwuid(os.getuid())[0],
                     command, filtermatch.name))
 
             obj = subprocess.Popen(command,