fix wrong openjdk checkout directory

[junyuanz1]

we will run into the following error when JDK_REPO, JDK_BRANCH, and OPENJDK_SHA are all set:

getOpenjdk:
     [echo]  Using user specified repo and branch
     [echo] git clone -q -b test#7642 https://ms-juniper@dev.azure.com/ms-juniper/Juniper/_git/jdk11u openjdktemp

BUILD FAILED
D:\a\1\openjdk-tests\TKG\scripts\build_test.xml:60: The following error occurred while executing this line:
D:\a\1\openjdk-tests\openjdk\build.xml:269: The following error occurred while executing this line:
D:\a\1\openjdk-tests\openjdk\build.xml:121: The directory D:\a\1\openjdk-tests\openjdk\openjdk-jdk does not exist

the checkout directory for the following line should be the git clone directory which is the openjdktemp

[smlambert]

thanks @junyuan-z 👍