skeleton: /etc/fstab: make sure /tmp is world writable and sticky

ramfs (which is used instead of tmpfs if CONFIG_SHMEM isn't enabled in the
kernel configuration), defaults to mode 0755 instead of 01777 like tmpfs
uses.

/tmp should be world writable and sticky, so explictly enforce the mode so
ramfs users gets it correct instead of relying on the defaults.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

system/skeleton/etc/fstab

@@ -5,5 +5,5 @@
 proc		/proc	       proc     defaults	  0	 0
 devpts		/dev/pts       devpts   defaults,gid=5,mode=620	  0	 0
 tmpfs           /dev/shm       tmpfs    mode=0777         0      0
-tmpfs           /tmp           tmpfs    defaults          0      0
+tmpfs           /tmp           tmpfs    mode=1777         0      0
 sysfs		/sys	       sysfs    defaults	  0	 0