Fix cache integrity check false-positives across multiple registries (#7595)

* Add tests for cache integrity check

* Always store sha1 hash as part of cacheIntegrity

This prevents broken installs as a result of a package being resolved
from a registry that does not return an sha512 integrity field, such as
an internal npm registry, where the package was previously cached from
a registry that did return a sha512 integrity hash.

* Improve cache integrity check error messages