Refactor: libcrmcommon: New pcmk__assert_alloc()

Wrapper for calloc() with NULL-check.

• Leave public and internal libraries alone where they currently NULL- check.
• Continue asserting in places where we already assert.
• Assert where we currently dereference the result without NULL-checking it, which should end in a seg fault.
• Always assert on failed memory allocation in daemons -- if they don't fail now, they will soon.
• Did not use with systemd_new_method() yet; perhaps something else might cause that to fail besides out-of-memory(?).

Signed-off-by: Reid Wahl <nrwahl@protonmail.com>