Simplify Weaver VTS test

- Get the config in SetUp() so that it's easily available to test cases.
- Rename "weaver" class member to "weaver_" to match coding style.
- Eliminate unnecessary variables when checking WeaverReadResponse.
- Fix a typo.

Bug: 291284381
Test: 'atest VtsHalWeaverTargetTest' on bramble
Change-Id: Ia6dca996103057bfdc9002bc9ab2c039e2333ed9