Use apex_name for the name of linker namespace

Till now short names are used for apex namespaces but there are no
explicit rule for this. Instead of extracting namespace name from apex
name (com.android.foo => foo), we'd better use apex name as it is
because it is well-established identifier for apexes.

Bug: 148826508
Test: build/flash/boot
      atest

Change-Id: I4f77eb85652a999274844436ba14b5c05831cf5b
3 files changed