Fix FsVerityTest to work with 32-bit ABI on 64-bit system

- Add 'compile_multilib: "both"' to FsVerityTestApp.  Without this,
  installation with the 32-bit ABI on a 64-bit system fails with
  error INSTALL_FAILED_NO_MATCHING_ABIS.

- Switch from SuiteApkInstaller to installPackage() in a @Before method.
  Without this, 'atest --all-abi FsVerityTest' does not work because the
  APK gets installed with the 64-bit ABI for the 64-bit test and then
  doesn't get reinstalled with the 32-bit ABI when the 32-bit test runs,
  causing the 32-bit test to be unable to find libfsveritytestapp_jni.so

Bug: 440971743
Bug: 442698909
Test: atest --all-abi FsVerityTest # on cf_x86_64_phone-trunk_staging-userdebug
Flag: EXEMPT TEST_ONLY
Change-Id: If70d4c0d549f641cfbb5349c89982904d66c7cd5