Restrict ptrace access by debuggerd and unconfineddomain.

Remove init, ueventd, watchdogd, healthd and adbd from the set of
domains traceable by debuggerd.  bionic/linker/debugger.cpp sets up
handlers for all dynamically linked programs in Android but this
should not apply for statically linked programs.

Exclude ptrace access from unconfineddomain.

Prohibit ptrace access to init via neverallow.

Change-Id: I70d742233fbe40cb4d1772a4e6cd9f8f767f2c3a
Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>