[CIVP-14018] civis_to_csv doesn't return a gzip when requested for include_header=False (#195)

* fix override of compression in civis_to_csv

* add test support for gzip compression

* gzip.compress is not available in 2.7

* remove local test script

* remove new cassettes and tests

* update docstring in civis_to_csv

Author: jkulzick

civis/io/_tables.py

@@ -326,8 +326,9 @@ def civis_to_csv(filename, sql, database, job_name=None, api_key=None,
     compression: str, optional
         Type of compression to use, if any. One of ``'none'``, ``'zip'``, or
         ``'gzip'``. Default ``'none'``. ``'gzip'`` currently returns a file
-        with no compression. In a future release, a ``'gzip'`` compressed
-        file will be returned.
+        with no compression unless include_header is set to False. In a
+        future release, a ``'gzip'`` compressed file will be returned for
+        all cases.
     delimiter: str, optional
         Which delimiter to use, if any. One of ``','``, ``'\t'``, or
         ``'|'``. Default: ``','``.
@@ -368,7 +369,7 @@ def civis_to_csv(filename, sql, database, job_name=None, api_key=None,
     # don't fix bug that would cause breaking change for now
     # when gzip compression is requested, a gzip file is not actually returned
     # instead the gzip file is decompressed during download
-    if compression == 'gzip':
+    if compression == 'gzip' and include_header:
         compression = 'none'
 
     # don't support parallel unload; the output format
@@ -915,8 +916,9 @@ def _download_file(url, local_path, headers, compression):
 
     # gzipped buffers can be concatenated so write headers as gzip
     if compression == 'gzip':
-        with open(local_path, 'wb') as fout:
-            fout.write(gzip.compress(headers))
+        with gzip.open(local_path, 'wb') as fout:
+            fout.write(headers)
+        with open(local_path, 'ab') as fout:
             shutil.copyfileobj(response.raw, fout, CHUNK_SIZE)
 
     # write headers and decompress the stream