In python3, these are iterators, which is fine in most situations. This
commit changes that places where it's not.

The code base contains a few unfornuate patterns such as:

    data = open(...).read()

OR

    fh = open(...)
    data = fh.read()

This causes a file descriptor leak as the opened file is never
explicitly closed again.  While slightly mitigated by CPython using
ref-counting and immediate closure, we should still update the code
to close the files.

This commit focuses on a large number of simple clean ups.  Most of
which relies on the "with open(...) as X" pattern where feasible.

As "with" causes identation noise, this commit deliberately refains
from "fixing" other suboptimal behaviour.  Notably there are several
instances of "except:" visible in the diff that should ideally be
reduced.
Signed-off-by: NNiels Thykier <niels@thykier.net>

It is shorter and more readable.

This was a regression introduced in 77dc9328Reported-by: NGianfranco Costamagna <locutusofborg@debian.org>

The only difference between the two versions was the function used to
parse the dependency.

For source-only uploads the fields should have been empty all along,
because there are no binary packages to include, but dpkg-genchanges
has incorrectly included all binary names that can be produced from
the debian/control template file (see #818618). Although DAK allows
an empty Binary field, the correct behavior should be for the field
to not be present if there are not binary packages to upload.

The affected packages broken by that field value are fixed since
Debian oldstable (Jessie). See also #759099.

Closes: #796213

This will be used by the signing service.

This lets us reject an upload up front rather than dying later in
process-upload.

Some other checks use it to see which architectures are included, for
example the previous commit.

For policy queues dak keeps the .buildinfo and .changes around until
the upload is processed.  As the uploads might already be sent to
buildds while waiting in the policy queue, the buildd upload might use
the same filename and end up getting rejected.  With this change, the
upload getting rejected should be the maintainer's upload.