Pass the master opts up to Salt API initialization.

If this is not done, the master configuration is loaded from the default system path ignoring any `--config-dir` directory passed to the `salt_master` when starting.

Fixes saltstack/salt#8917
Rename `master_config` to `opts` for consistency.

Updated remaining `APIClient` initializations to include the passed `opts` dictionary.
Merge pull request #85 from s0undt3ch/master

Pass the master opts up to Salt API initialization.