New infrastructure to switch remaining commands to "cmd" calls.

This introduces a new feature of the IBinder command protocol
to allow the shell command implementation to call back into
its caller to ask it to open files in the calling context.  This
is needed so that commands that have arguments specifying files
can open those files as the calling shell, not the system (or
whatever) process.

To test this all out, move the "am start" implementation over
to ActivityManagerShellCommand, in particular along with its
option to specify a file in which to write profiling data.

Test: Manual

Change-Id: I0c1e3857defefbd19a2ac29413aafbb34b1e48a3