In my system I had a configuration like:
```
{
"experimental": {
"parallel-instances": true,
"snapd-snap": true
},
"proxy": null,
"seed": {
"loaded": true
}
}
```
which lead to a crash on startup of master.
interfaces/policy: minimal policy check for replacing sanitizeReservedFor helpers (1/2)
Add InstallCandidateMinimalCheck to policy checks. The check will be activated for snap installation when snap is installed with --dangerous flag and it's aim is to check slot snap type restrictions only. It doesn't check plugs or slot attributes and doesn't return the default policy decision from base declaration (i.e. deny-installation: true) which would effectively prevent --dangerous. This policy check is meant to replace existing sanitizeSlotReservedFor* helpers and therefore is semantically an equivalent of these helpers.
This new policy check is not yet active in this PR, it will get enabled in a followup together with the removal of sanitizeSlotReservedFor.. helpers.