Fix command line args for test runner

[jmglov]

Fixes #78

$ bb test --only babashka.cli-test/exec-args-replaced-test
Running tests in #{"test"}
Testing babashka.cli-test
Ran 1 tests containing 2 assertions.
0 failures, 0 errors.

$ bb test --only babashka.cli-test
Running tests in #{"test"}
Testing babashka.cli-test
Ran 15 tests containing 107 assertions.
0 failures, 0 errors.

$ bb test --vars babashka.cli-test/exec-args-replaced-test
Running tests in #{"test"}
Testing babashka.cli-test
Ran 1 tests containing 2 assertions.
0 failures, 0 errors.

$ bb test --vars babashka.cli-test/exec-args-replaced-test babashka.cli-test/error-fn-test 
Running tests in #{"test"}
Testing babashka.cli-test
Ran 2 tests containing 3 assertions.
0 failures, 0 errors.

$ bb test
Running tests in #{"test"}
Testing babashka.cli.exec-test
Testing babashka.cli-test
Ran 16 tests containing 122 assertions.
0 failures, 0 errors.