Use local-build corehost.exe
This is staying in the repo, so we can copy the local-built version.
Copy deps and deps.json, make sure corehost temp dir exists
Add additional runtimes to the sharedframework's project.json
Delete an unused file, modify crossgen target condition
* sharedhost\project.json is unused. It is copied from the local build.
* the crossgen target was conditioned on an environment variable, but the
variable could be set to anything. Instead, make sure it is either
"true" or "1".
Use stage2 instead of stage0 for shared framework restore
