PMM-7 Run supervisor as pmm during build

[ademidoff]

PMM-7

Link to the Feature Build: SUBMODULES-3770

This PR is meant to solve the problem we are currently seeing at build time, during the execution of the ansible dashboards role:

# supervisorctl stop grafana
"stdout": "grafana: ERROR (not running)"

# supervisorctl remove grafana
"stdout": "ERROR: process/group still running: grafana"

The problem is most probably due to the fact that we do not start supervisord as pmm, so it ends up being unable to stop a process owned by root. This leads to an eventual pipeline failure resulting in an interrupted build.

The issues is not reproducible in 100% of builds, but may still be affecting more than 50% of v3 builds.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 43.53%. Comparing base (9369be0) to head (88fba9f).
Report is 1 commits behind head on v3.

Additional details and impacted files

@@            Coverage Diff             @@
##               v3    #3309      +/-   ##
==========================================
+ Coverage   43.50%   43.53%   +0.03%     
==========================================
  Files         366      366              
  Lines       44162    44162              
==========================================
+ Hits        19211    19228      +17     
+ Misses      23270    23254      -16     
+ Partials     1681     1680       -1     

Flag	Coverage Δ
admin	11.47% <ø> (ø)
agent	51.96% <ø> (+0.12%)	⬆️
managed	45.25% <ø> (+0.01%)	⬆️
vmproxy	68.57% <ø> (ø)

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