Add **kwargs parameters to _mkdir, _cat_file, adhere to fsspec API

[krfricke]

These two methods don't accept **kwargs parameters, which makes them incompatible with libraries utilizing the abstract API. For example, pyarrow 6.0.1 fails for create dir:

import fsspec
import pyarrow.fs

fs = fsspec.filesystem("gs")
wrapped = pyarrow.fs.PyFileSystem(pyarrow.fs.FSSpecHandler(fs))
wrapped.create_dir("bucket/test", recursive=True)

with

  File "pyarrow/_fs.pyx", line 461, in pyarrow._fs.FileSystem.create_dir
  File "pyarrow/_fs.pyx", line 1129, in pyarrow._fs._cb_create_dir
  File "/Users/kai/.pyenv/versions/3.7.7/lib/python3.7/site-packages/pyarrow/fs.py", line 341, in create_dir
    self.fs.mkdir(path, create_parents=recursive)
  File "/Users/kai/.pyenv/versions/3.7.7/lib/python3.7/site-packages/fsspec/asyn.py", line 85, in wrapper
    return sync(self.loop, func, *args, **kwargs)
  File "/Users/kai/.pyenv/versions/3.7.7/lib/python3.7/site-packages/fsspec/asyn.py", line 47, in sync
    coro = func(*args, **kwargs)
TypeError: _mkdir() got an unexpected keyword argument 'create_parents'

Closes #404

[martindurant]

Wouldn't it be better if we actually supported create_parents? For gcsfs, this would mean creating the bucket, if it doesn't already exist.

[krfricke]

I think this PR is more about adhering to the fsspec API for forward compatibility. If creating an empty bucket is desired behavior for this API, this should probably be addressed in a different PR.

[martindurant]

create_parents is in the spec signature, though: https://github.com/fsspec/filesystem_spec/blob/master/fsspec/spec.py#L245

[krfricke]

The problem is that it is indeed part of the fsspec API: https://github.com/fsspec/filesystem_spec/blob/master/fsspec/asyn.py#L737-L738

    async def _mkdir(self, path, create_parents=True, **kwargs):
        pass  # not necessary to implement, may not have directories

but is not implemented in gcsfs: https://github.com/fsspec/gcsfs/blob/main/gcsfs/core.py#L606-L611

    async def _mkdir(
        self,
        bucket,
        acl="projectPrivate",
        default_acl="bucketOwnerFullControl",
        location=None,
    ):

(and mkdir is just the sync wrapper for _mkdir: https://github.com/fsspec/gcsfs/blob/main/gcsfs/core.py#L650)

[martindurant]

Right, so instead of ignoring it with **kwargs, I am suggesting that now would be a good time to implement it - right in this PR.

[krfricke]

I'm not familiar with gcs internals/API, so if someone would like to add to this PR, please go ahead.

[krfricke]

Or is it literally just removing these two lines if create_parents=True:

        if "/" in bucket:
            return

[martindurant]

How about that?

[krfricke]

Thanks!