createhdds: use temp file correctly when uploading

Summary:
With the previous code, the temporary file wasn't closed before
we try to upload its contents to the disk image. This seems to
cause problems when run in Python 2; the file is truncated on
upload. So rejig things a bit so we use tempfile.mkstemp, close
the file after writing to it, then remove it ourselves after
doing the upload. Tested with Python 2 and Python 3 that this
creates a correct image.

If something goes wrong at the wrong time the temp file will
be left around, but hey, it's a temp file - they get cleaned
up on system shutdown. So doesn't seem like a big deal.

Test Plan:
Check building the two images that involve a file
upload in both Python 2 and Python 3, make sure the file is
complete and correct in all cases.

Reviewers: jskladan, garretraziel

Reviewed By: garretraziel

Subscribers: tflink

Differential Revision: https://phab.qadevel.cloud.fedoraproject.org/D786

createhdds.py

@@ -147,7 +147,8 @@ class GuestfsImage(object):
             for upload in self.uploads:
                 # download the file to a temp file - borrowed from
                 # fedora_openqa_schedule (which stole it from SO)
-                with tempfile.NamedTemporaryFile(prefix="createhdds") as dltmpfile:
+                (_, tmpfname) = tempfile.mkstemp(prefix="createhdds")
+                with open(tmpfname, 'wb') as tmpfh:
                     resp = urlopen(upload['source'])
                     while True:
                         # This is the number of bytes to read between buffer
@@ -155,12 +156,13 @@ class GuestfsImage(object):
                         buff = resp.read(8192)
                         if not buff:
                             break
-                        dltmpfile.write(buff)
+                        tmpfh.write(buff)
                 # as with write, the dict must specify a target
                 # partition and location ('target')
                 partn = gfs.list_partitions()[int(upload['part'])-1]
                 gfs.mount(partn, "/")
-                    gfs.upload(dltmpfile.name, upload['target'])
+                gfs.upload(tmpfname, upload['target'])
+                os.remove(tmpfname)
             # we're all done! rename to the correct name
             os.rename(tmpfile, self.filename)
         except:
@@ -170,7 +172,8 @@ class GuestfsImage(object):
             raise
         finally:
             # whether things go right or wrong, we want to close the
-            # gfs instance
+            # gfs instance, and rwmj recommends 'shutdown()' too
+            gfs.shutdown()
             gfs.close()