Version guard Application.onCreate strict mode fix

In I30b3eafa4a833fc42d0a938da9446007ade80480 we fixed an outstanding bug
around clobbering strict mode in Application.onCreate and allowing disk
writes to go unreported.

This guards that fix to only take effect once an app targets > SDK 26
and applies a ThreadPolicy inside Application.onCreate.

Bug: 63436909
Test: Ran apps with violations
Change-Id: Ib0ac1626e2ef322c4e61bbdf493d1f724b08652d