Test purge-keys with views

Test purge-keys with views

Create a test scenario where a signed zone is in multiple views and
then a key may be purged. This is a bug case where the key files are
removed by one view and then the other view starts complaining.

Note: This commit was manually modified because 9.18 does not have
pytest based kasp system tests. The test was translated to a shell
script style test case.

(cherry picked from commit 752d8617f558130cc552cae0e903aca318a3ef02)