ci: Fix pip upgrade warning

[theopolis]

Pip is warning us that a newer version is available.

Installing collected packages: psutil, timeout-decorator, six, thrift, argparse, future, osquery, pywin32
    Running setup.py install for timeout-decorator: started
    Running setup.py install for timeout-decorator: finished with status 'done'
    Running setup.py install for thrift: started
    Running setup.py install for thrift: finished with status 'done'
    Running setup.py install for future: started
    Running setup.py install for future: finished with status 'done'
Successfully installed argparse-1.4.0 future-0.18.2 osquery-3.0.6 psutil-5.7.2 pywin32-228 six-1.15.0 thrift-0.11.0 timeout-decorator-0.4.1
python.exe : WARNING: You are using pip version 20.1.1; however, version 20.2 is available.
At D:\a\_temp\e56a42ad-24b7-444f-a585-4f96f7940dbd.ps1:5 char:1
+ & $python3_path\python -m pip install setuptools psutil timeout_decor ...
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : NotSpecified: (WARNING: You ar...2 is available.:String) [], RemoteException
    + FullyQualifiedErrorId : NativeCommandError
 
##[error]PowerShell exited with code '1'.

One solution is to upgrade pip before using it.

[Smjert]

Something I failed to mention in the past: I have configured Azure Pipelines to build master every 4 hours, to be able (if looking at it!) to catch these kind of failures earlier, or at least see if they were repeatable.
So if you have a look here https://dev.azure.com/trailofbits/osquery/_build?definitionId=6&branchFilter=50%2C50%2C50%2C50%2C50%2C50%2C50%2C50%2C50%2C50%2C50%2C50%2C50%2C50%2C50%2C50 (filtered by master branch) and on the left look for Scheduler for, you'll see that there's a lot of failures since Friday

[theopolis]

@Smjert, this fixes the issue but it may not be the only (or best) method.

[directionless]

Seems fine, if potentially slow. Dunno if you want to wait for @Smjert for it

[Smjert]

Thanks for looking into this!

I did some tests and noticed that the situation changed when they updated the agent image version.
Python went from 3.8.4 to 3.8.5 but I don't think this is the issue because the warning about pip was already showing previously (although it's true that it's a NativeCommandError...).
Moreover I tested in a local VM with both Python versions, either directly inside powershell shell or a script and the process, despite the warning, never fails.
They must've changed something in the powershell task or in the powershell configuration.

The powershell task has a failOnStdErr that should have the task fail if something is written to stderr, although by default it's at false.
I tried on my Azure Pipeline instance to explicitly set it to false, but the failure is still there.

Long story short there's something strange going on, but I think we can wait to maybe better look into it; meanwhile this is a valid workaround, and it doesn't seem to slow down much, if at all.