Refactor: libraries: move health strategy validation function

... from lib/pengine/common.c to lib/common/health.c, for logical grouping of
code related to node health.

It is moved to libcrmcommon rather than a new source file in lib/pengine
because lib/pengine/common.c is used by both libpe_status and libpe_rules.
Everything will eventually be moved into libcrmcommon anyway ...