scripts: container: Fix 'exec' command line parsing.

* guix/scripts/container/exec.scm (partition-args): Reimplement such
  that all args up to and including the PID are returned as the first of
  the two values.

import: pypi: add updater

* guix/import/pypi.scm (guix-package->pypi-name,
  latest-release): New procedures.
  (%pypi-updater): New variable.
* guix/scripts/refresh.scm (%updaters): Add %PYPI-UPDATER.
* doc/guix.texi (Invoking guix refresh): Mention PyPI

gnu: Add python-tempest-lib.

* gnu/packages/openstack.scm (python-tempest-lib,
  python2-tempest-lib): New variables.

gnu: python-oslotest: move mox3 to the propagated-inputs

* gnu/packages/openstack.scm (python-oslotest): move mox3 to the propagated
  inputs.

gnu: Add python-oslo.log.

* gnu/packages/openstack.scm (python-oslo.log,
  python2-oslo.log): New variables.

gnu: paramiko: Move python-pycrypto to the propagated inputs.

* gnu/packages/python.scm (python-paramiko): Move python-pycrypto to the
  propagated-inputs.

gnu: Add python-os-testr.

* gnu/packages/openstack.scm (python-ostestr,
  python2-ostestr): New variables.

gnu: Add python-oslosphinx.

* gnu/packages/openstack.scm (python-oslosphinx,
  python2-oslosphinx): New variables.

gnu: Add python-hacking.

* gnu/packages/openstack.scm (python-hacking,
  python2-hacking): New variables.

gnu: Add python-flake8-2.2.4

* gnu/packages/python.scm (python-flake8-2.2.4,
  python2-flake8-2.2.4): New variables.

gnu: Add python-mccabe 0.2.1

* gnu/packages/python.scm (python-mccabe-0.2.1,
  python2-mccabe-0.2.1): New variables.

gnu: Update python-requests.

* gnu/packages/python.scm (python-requests, python2-requests): Bump to 2.8.0.

import: pypi: Use "pypi-uri" instead of building the URL manually.

* guix/import/pypi.scm (make-pypi-sexp): Use "pypi-uri".
* tests/pypi.scm: Update the tests accordingly.

guix: Add a "pypi-uri" helper method.

* guix/download.scm (mirrors): New "pypi" mirror.
* guix/build-system/python.scm (pypi-uri): New method.

gnu: Add esmtp.

* gnu/packages/mail.scm (esmtp): New public variable.

gnu: Add libesmtp.

* gnu/packages/mail.scm (libesmtp): New public variable.

system: Rename (gnu system linux) to (gnu system pam).

* gnu/system/linux.scm: Rename to...
* gnu/system/pam.scm: ... this.
* gnu-system.am (GNU_SYSTEM_MODULES): Adjust accordingly.
* gnu.scm, gnu/services/base.scm, gnu/services/desktop.scm,
  gnu/services/networking.scm, gnu/services/ssh.scm,
  gnu/services/xorg.scm, gnu/system.scm, gnu/system/vm.scm: Likewise.

services: Add 'guix-publish-service'.

* gnu/services/base.scm (<guix-publish-configuration>): New record
  type.
  (guix-publish-dmd-service): New procedure.
  (%guix-publish-accounts, guix-publish-service-type): New variables.
  (guix-publish-service): New procedure.
* doc/guix.texi (Invoking guix publish): Add xref to
  'guix-publish-service' anchor.
  (Base Services): Document 'guix-publish-service'.

scripts: environment: Display friendly container error messages.

* guix/scripts/environment.scm (assert-container-features): New
  procedure.
  (guix-environment): Use it.

build: container: Add feature test predicates.

* gnu/build/linux-container.scm (user-namespace-supported?,
  unprivileged-user-namespace-supported?, setgroups-supported?): New
  procedures.
* tests/container.scm: Use predicates.
* tests/syscalls.scm: Likewise.