Fail the RPM build if FPM tool is not present

[NikolaMilosavljevic]

Currently, if the build is supposed to produce RPM packages, but the tooling (i.e. fpm) is missing, a message will be logged and the build will skip the RPM package generation. This can result in successful builds that are missing the required artifacts.

Additional changes were needed, as RPM targets were being executed for any build that was running on RPM-based distro due to:

installer/src/redist/targets/GenerateRPMs.targets

Line 19 in fa82557

Condition=" '$(IsRPMBasedDistro)' == 'True' "

The use of property IsRPMBasedDistro was overloaded to mean both that the distro is RPM-based and that we want to build installers.

Property was set here:

installer/src/redist/targets/GetRuntimeInformation.targets

Lines 27 to 28 in fa82557

	<IsRPMBasedDistro Condition=" $(HostRid.StartsWith('rhel')) AND '$(HostRid)' != 'rhel.6-x64' ">true</IsRPMBasedDistro>
	<IsRPMBasedDistro Condition=" $(HostRid.StartsWith('centos')) ">true</IsRPMBasedDistro>

For installer build we were passing this same property, which was already being set on rpm-based distros, so this wasn't correct:

installer/.vsts-pr.yml

Line 250 in fa82557

additionalBuildParameters: '/p:PublishBinariesAndBadge=false /p:IsRPMBasedDistro=true'

I am now setting a different property, BuildSdkRpm, in scenarios where RPM packaging is desired. This matches DEB build experience, where we have a similar pair of properties: BuildSdkDeb and IsDebianBaseDistro.

Notes

Fix for 8.0.1xx - will be backported to other 8.0.x branches in support. Separate fix will be made for 9.0.

Contributes to #20561

[NikolaMilosavljevic]

Failure in source-build and regular (non-pkg) Linux leg - neither of these should even attempt to build RPM packages, but that's what's happening. More changes are needed.

[NikolaMilosavljevic]

Pushed a fix.

[NikolaMilosavljevic]

This is now passing all checks - @marcpopMSFT is there a reason not to merge this yet? Same for 9.0 change: dotnet/sdk#51170

[marcpopMSFT]

Branch is still open so we can merge.