MINIFICPP-1071 - Fix variable substitution on Windows build script

Signed-off-by: Arpad Boda <aboda@apache.org>

This closes apache#667

win_build_vs.bat

@@ -64,10 +64,10 @@ cd %builddir%\
 
 
 cmake -G %generator% -DCMAKE_BUILD_TYPE_INIT=%cmake_build_type% -DCMAKE_BUILD_TYPE=%cmake_build_type% -DWIN32=WIN32 -DENABLE_LIBRDKAFKA=%build_kafka% -DENABLE_JNI=%build_jni% -DOPENSSL_OFF=OFF -DENABLE_COAP=%build_coap% -DUSE_SHARED_LIBS=OFF -DDISABLE_CONTROLLER=ON  -DBUILD_ROCKSDB=ON -DFORCE_WINDOWS=ON -DUSE_SYSTEM_UUID=OFF -DDISABLE_LIBARCHIVE=ON -DDISABLE_SCRIPTING=ON -DEXCLUDE_BOOST=ON -DENABLE_WEL=TRUE -DFAIL_ON_WARNINGS=OFF -DSKIP_TESTS=%skiptests% .. && msbuild /m nifi-minifi-cpp.sln /property:Configuration=%build_type% && copy main\release\minifi.exe main\
-if [cpack] EQU [ON] ( 
+if [%cpack%] EQU [ON] ( 
 	cpack
     )
-if [skiptests] NEQ [OFF] ( 
+if [%skiptests%] NEQ [ON] ( 
 	ctest -C %build_type%
 	IF %ERRORLEVEL% NEQ 0 EXIT %ERRORLEVEL%
 	)
@@ -76,4 +76,4 @@ goto :eof
 
 :usage
 @echo "Usage: %0 <build_dir> options"
-exit /B 1
+exit /B 1