[SPARK-3808] PySpark fails to start in Windows

Modified syntax error of *.cmd script.

Author: Masayoshi TSUZUKI <tsudukim@oss.nttdata.co.jp>

Closes #2669 from tsudukim/feature/SPARK-3808 and squashes the following commits:

7f804e6 [Masayoshi TSUZUKI] [SPARK-3808] PySpark fails to start in Windows

bin/compute-classpath.cmd

@@ -38,7 +38,7 @@ if exist "%FWDIR%conf\spark-env.cmd" call "%FWDIR%conf\spark-env.cmd"
 rem Build up classpath
 set CLASSPATH=%SPARK_CLASSPATH%;%SPARK_SUBMIT_CLASSPATH%
 
-if "x%SPARK_CONF_DIR%"!="x" (
+if not "x%SPARK_CONF_DIR%"=="x" (
   set CLASSPATH=%CLASSPATH%;%SPARK_CONF_DIR%
 ) else (
   set CLASSPATH=%CLASSPATH%;%FWDIR%conf