Add shill user to debugfs-access group.

This CL is in preparation to run the shill process tree as a non-root
user.

debugfs-access group has read access to /sys/kernel/debug. Shill needs
to read from /sys/kernel/debug/ieee80211/<interface>/queues as part of
wifi monitoring. See
src/aosp/system/connectivity/shill/wifi/mac80211_monitor.cc:129:
https://cs.corp.google.com/chromeos_public/src/aosp/system/connectivity/shill/wifi/mac80211_monitor.cc?rcl=e940876477cc07e8c38a329c0808fb0fb3880477&l=129

CQ-DEPEND=CL:1003329
BUG=chromium:649417
TEST=tested as part of larger shill sandbox debug CL

Change-Id: Ia216387e12b14a42699598b5738cf3373114f848
Reviewed-on: https://chromium-review.googlesource.com/1003325
Commit-Ready: Micah Morton <mortonm@chromium.org>
Tested-by: Micah Morton <mortonm@chromium.org>
Reviewed-by: Ben Chan <benchan@chromium.org>
Reviewed-by: Kevin Cernekee <cernekee@chromium.org>
diff --git a/profiles/base/accounts/group/debugfs-access b/profiles/base/accounts/group/debugfs-access
index 7f8c834..ed2b6a7 100644
--- a/profiles/base/accounts/group/debugfs-access
+++ b/profiles/base/accounts/group/debugfs-access
@@ -1,3 +1,3 @@
 group:debugfs-access
 gid:605
-users:
+users:shill