Low: tools: improve how crm_node -R purges node from CIB

Rename cib_remove_node() to purge_node_from_cib(), add a doxygen block,
make the argument order consistent with similar functions, make it return a
standard code, and improve variable names, log messages, and formatting.
Set the exit code in caller rather than for each error return.

Previously, the node was purged from the CIB twice, once after purging it from
the fencer and again after purging it from the attribute manager. Now, just
purge once, at the end.

Previously, cib_new() and signon() were not checked for error, and the request
XML was never freed. Now, they are.