vts: Correct the test RSA key format

The format of test key was not PKCS8.
Correct it and add the generating command for reference.

Fixed: 181701819
Test: VtsHalKeymasterV4_0TargetTest --gtest_filter=*strongbox*
Change-Id: I7793c781eee976bc813b6fea77762b173f95e06a
1 file changed