Log: executor,fencing: improve action flag messages

... instead of using set_bit()/clear_bit(), which improves trace messages
like:

Bit 0x00000001 set by some_function:100

to:

Action flags 0x00000001 (SVC_ACTION_LEAVE_GROUP) for some_action set by some_function:100

This uses pcmk__set_flags_as() directly rather than creating a macro wrapper,
because there is no internal libcrmservice header currently, and the long-term
intent is to merge libcrmservice into libcrmcommon, so this can be revisited
then.