Allow the shell user to set debug.* properties.
This allows systrace to work on Android.

Allow the shell user to set sys.powerctl, to allow reboots
to work.

Addresses the following denials:

<4>[ 2141.449722] avc:  denied  { set } for property=debug.atrace.tags.enableflags scontext=u:r:shell:s0 tcontext=u:object_r:debug_prop:s0 tclass=property_service
<4>[ 2141.450820] avc:  denied  { set } for property=debug.atrace.app_cmdlines scontext=u:r:shell:s0 tcontext=u:object_r:debug_prop:s0 tclass=property_service
<4>[ 2141.506703] avc:  denied  { set } for property=debug.atrace.tags.enableflags scontext=u:r:shell:s0 tcontext=u:object_r:debug_prop:s0 tclass=property_service
<4>[ 2141.507591] avc:  denied  { set } for property=debug.atrace.app_cmdlines scontext=u:r:shell:s0 tcontext=u:object_r:debug_prop:s0 tclass=property_service

Bug: 12231073
Change-Id: Iaba1db06ba287c7d5d10ce287833c57238e03bb6