Export TestContext in minio-macros

[b-kamphorst]

Hi! I'm very enthusiastic about the upcoming release of minio-macros (#170) and already started experimenting with it. However, I am currently unable to import minio_common::test_context::TestContext as advocated in the documentation. Perhaps this still needs to be re-exported in minio-macros?

[b-kamphorst]

Ah turns out I made a mistake installing minio_common. The crate naming is inconsistent:

minio-macros = { git = "https://github.com/minio/minio-rs" }
minio_common = { git = "https://github.com/minio/minio-rs" }

Regardless, I wonder whether it is valuable to avoid the direct import of minio_common.

Other suggestions, assuming that you want to publish the test functionality:

1. make it very explicit that this fixture uses the public minio playground and persists state there,
2. change the logic around DEFAULT_SSL_CERT_FILE to avoid IOError that this path is not found (even if the cert check is ignored).