Mapistore rest fixes

This pull request includes a fix in the MAPIStore Python bindings and some corrections in the REST API.

* There were some remaining magic values in _rest.py_ that could be replaced by values in the MAPIStore Python bindings.
* In the @set_properties@ methods, the dictionary update could be done more efficiently.
* Several functions unnecessarily modified their arguments, which is error-prone.
short answer: it does and it does not. Only when logging to a file. So if you execute samba with `-i` you won't get it.

long answer: DEBUG macro is:

    #define DEBUG( level, body ) \
      (void)( ((level) <= MAX_DEBUG_LEVEL) && \
    	  unlikely(DEBUGLEVEL_CLASS[ DBGC_CLASS ] >= (level))		\
           && (dbghdrclass( level, DBGC_CLASS, __location__, __FUNCTION__ )) \
           && (dbgtext body) )

That means dbghdrclass + dbgtext. If we check dbghdrclass function we'll see:


	/* Don't print a header if we're logging to stdout. */
	if ( state.logtype != DEBUG_FILE ) {
		return( true );
	}

More info in `samba/include/util/debug.h|c`