Limit VENDOR_TEST_REPOS git clone based on BUILD_LIST

[llxia]

Due to the increasing popularity of VENDOR_TEST_REPOS, we should Limit VENDOR_TEST_REPOS git clone based on BUILD_LIST. That is only git clone the related repos. This will help us to increase the efficiency of the test pipeline. For example, if VENDOR_TEST_REPOS is set to functional and system test repo, for the test build that runs perf testing (i.e., BUILD_LIST=perf), neither functional or system repos should be git cloned.