Add create() contract test that verifies ancestor dir creation

The semantics of FileSystem#create() appear to include implicit creation of any parent or ancestor directories in the Path being created, unlike Posix filesystems, which expect the parent directory to already exist.

S3AFileSystem does implicitly create ancestor directories. It does not currently enforce that any ancestors are directories (HADOOP-13221).

Deliverable for this JIRA is just a test case added to AbstractContractCreateTest which verifies that missing ancestors are created by create().

Pulling this test dev work out into separate jira from HADOOP-14457.