mtools-native: disable reading host configs

Removed code that reads /etc/mtools.conf, /etc/default/mtools.conf,
/etc/mtools and /etc/default/mtools to ensure that mtools output
doesn't depend on the global host configs.

It's still possible to use ~/.mtoolsrc config or point MTOOLSRC
environment variable to any configuration file if user want
to configure mtools.

(From OE-Core rev: 868cb638c92f650a2f0bea9669b68c1e8aebabab)

Signed-off-by: Ed Bartosh <ed.bartosh@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-devtools/mtools/mtools/disable-hardcoded-configs.patch

@@ -0,0 +1,23 @@
+Disabled reading host configs.
+
+Upstream-Status: Pending
+
+Signed-off-by: Ed Bartosh <ed.bartosh@linux.intel.com>
+
+--- mtools-4.0.18/config.c.orig	2017-06-13 12:27:38.644000000 +0300
++++ mtools-4.0.18/config.c	2017-06-13 12:28:47.576000000 +0300
+@@ -701,14 +701,6 @@
+ 	memcpy(devices, const_devices,
+ 	       nr_const_devices*sizeof(struct device));
+ 
+-    (void) ((parse(CONF_FILE,1) |
+-	     parse(LOCAL_CONF_FILE,1) |
+-	     parse(SYS_CONF_FILE,1)) ||
+-	    (parse(OLD_CONF_FILE,1) |
+-	     parse(OLD_LOCAL_CONF_FILE,1)));
+-    /* the old-name configuration files only get executed if none of the
+-     * new-name config files were used */
+-
+     homedir = get_homedir();
+     if ( homedir ){
+ 	strncpy(conf_file, homedir, MAXPATHLEN );

meta/recipes-devtools/mtools/mtools_4.0.18.bb

@@ -33,6 +33,7 @@ SRC_URI = "${GNU_MIRROR}/mtools/mtools-${PV}.tar.bz2 \
            file://0001-Continue-even-if-fs-size-is-not-divisible-by-sectors.patch \
            "
 
+SRC_URI_append_class-native = " file://disable-hardcoded-configs.patch"
 
 inherit autotools texinfo