Catch missed POST in sanity checker
Inject tool installers into JENKINS_HOME instead of waiting to be fetched from update center the normal way

Attaching a list of alternatives that does not work:

- Declaring tool version regardless of updates not present will fail the build. Basically just postpones waiting from pre-configuration to pre-build.
- Using /pluginManager/checkUpdatesServer in newer Jenkins releases seems to be reliable but it still can take several minutes for updates to be available.
- Checking for updates the standard way is slow, see above.