Various fixes to fopen mode handling in SFTP Stream
* bantu/SFTPStreamTest:
Explicitly set size to 0 when creating or truncating.
mode[0] of 'c' is not supposed to truncate.
Need to create the file when it does not exist and mode[0] is not 'r'.
Add SFTPStreamTest::testFopenFcloseCreatesFile()
Conflicts:
tests/Functional/Net/SFTPLargeFileTest.php