validate_frontend_configuration is exactly check_command_execute, so just use
it.

Replace trafficserver_cache_availability with check_command_execute which
has the same functionality.

The eventual message from trafficserver_cache_availability will be visible
anyway.

publish-failsafe-error-promise and promise-key-download-url-ready shall be
less reactive, as otherwise it results with constant problems detection on
the running cluster, by raising tickets. When those promises are less
sensitive it gives time for the cluster to stabilize.

See merge request !1693

Following advice from https://luajit.org/download.html use recent commit id,
but rely on github archive.

Drop obsoleted patch, enforce --with-shared-termcap-library

Also use directly archive with patches.

Changes:
 * use xz archive
 * stabilize patch name
 * update patch to current version