Reduce impact of org.gnome.SessionManager slow-down / freeze (issue 277)

[fohrloop]

This provides a partial solution to #277

Previously: Using the org.gnome.SessionManager method repeatedly would
freeze system in 400-600 iterations.

Now: Get to ~2000 iterations before system freezes EDIT: Get until 2000 iterations until mouse starts to feel laggy. It will finish even 10k iterations without freezing, but mouse is permanently laggy (until reboot).

Contents

• Dbus connections are now closed. In addition, gc.collect() is called
  each time connection is closed (at least for now), as adding it helped
  to get more iteration cycles.
• Add warning to docs of org.gnome.SessionManager
• bonus: Some refactoring of dbus adapter tests + remove the temporary
  warning ignore introduced in Fix: org.gnome.SessionManager RuntimeError (Issue 276) #278.

[fohrloop]

Hmm. Getting

ERROR: THESE PACKAGES DO NOT MATCH THE HASHES FROM THE REQUIREMENTS FILE. If you have updated the package versions, please update the hashes. Otherwise, examine the package contents carefully; someone may have tampered with them.
    unknown package:
        Expected sha256 e5952d2d18b79f7dc25e62e014fe5a23eb1a3d2bc66318df8988a01b1a037c5b
             Got        eb29664371e4272ecce4f08be5989c14d72e3e5163f8d4681824ed5fa8e02e3e

on python 3.7 tests on ubuntu-latest. Checking from the logs, I can see it downloaded

Downloading mypy-1.4.1-cp37-cp37m-manylinux_2_17_x86_64.manylinux2014_x86_64.whl (11.6 MB)

and looking from the pypi page for mypy 1.4.1 for mypy-1.4.1-cp37-cp37m-manylinux_2_17_x86_64.manylinux2014_x86_64.whl the hashes really are:

Algorithm	Hash digest	
SHA256	e5952d2d18b79f7dc25e62e014fe5a23eb1a3d2bc66318df8988a01b1a037c5b	Copy
MD5	50d22678fb4866fde066dbb0282c8db3	Copy
BLAKE2b-256	65f777339904a3415cadca5551f2ea0c74feefc9b7187636a292690788f4d4b3	Copy

so the expected hash is correct and what was got is wrong.. Investigating.

Update

The issue was resolved by simply re-running the job. However, if this starts to happen often, perhaps should check the version(s) of pip used, as using too old or new version of pip seems to be culprit.