Refactor the shell domains.

Originally we used the shell domain for ADB shell only and
the init_shell domain for the console service, both transitioned
via automatic domain transitions on sh.  So they originally
shared a common set of rules.  Then init_shell started to be used
for sh commands invoked by init.<board>.rc files, and we switched
the console service to just use the shell domain via seclabel entry
in init.rc.  Even most of the sh command instances in init.<board>.rc
files have been converted to use explicit seclabel options with
more specific domains (one lingering use is touch_fw_update service
in init.grouper.rc).  The primary purpose of init_shell at this point
is just to shed certain permissions from the init domain when init invokes
a shell command.  And init_shell and shell are quite different in
their permission requirements since the former is used now for
uid-0 processes spawned by init whereas the latter is used for
uid-shell processes spawned by adb or init.

Given these differences, drop the shelldomain attribute and take those
rules directly into shell.te.  init_shell was an unconfined_domain(),
so it loses nothing from this change.  Also switch init_shell to
permissive_or_unconfined() so that we can see its actual denials
in the future in userdebug/eng builds.

Change-Id: I6e7e45724d1aa3a6bcce8df676857bc8eef568f0
Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>