diag: Remove world read/write permissions from /dev/diag

/dev/diag has world read/write permissions which is considered
a security risk.  Remove these permissions.  Add new qcom_diag
group for access to /dev/diag

CRs-Fixed: 356415
(cherry picked from commit 14c85ec56fd47c5eb143617a3bd5a6e7ee39cb6e)

Change-Id: I536323a97e19a07bbd8eadffa0265d1955590285

Conflicts:
	include/private/android_filesystem_config.h

 Author:    Dixon Peterson <dixonp@codeaurora.org>
 On branch android-4.4
 Changes to be committed:
	modified:   include/private/android_filesystem_config.h
	modified:   rootdir/init.rc
	modified:   rootdir/ueventd.rc