install copy of shell in vendor partition

install copy of shell in vendor partition

This is to be used by vendor processes. Particularly, vendor shell
scripts that get launched as init services. The shell is restricted from
running as interactive mode in SEPolicy. Unless it is launched from rooted
system shell. The change also adds the ability to override the default
$PATH regardless of the environment.

Bug: 36463595
Test: Boot sailfish with new shell and ensure all init services exit
      with status 0

Change-Id: I1eaf2c8a8f6905caf00d53e067add67eaea00e09
Signed-off-by: Sandeep Patil <sspatil@google.com>