Update test_B7_persist_temp_file
Update test_B7_persist_temp_file

Add a test case for persisting a file with custom permissions

Signed-off-by: Teodora Sechkova <e7a2b861183aa3bdb0c9acf2cae91c9cd14116e3@vmware.com>

secure-systems-lab/securesystemslib,secure-systems-lab/securesystemslib