Fix use_embedded_native_libs handling for android_test

`use_embedded_native_libs: true` should cause
`--extract-native-libs=false` be added to the manifest_fixer invocation,
and it was not happening.
There are also minor naming improvements.

Bug: 117618214
Test: treehugger and 'atest CtsDynamicLinkerTestCases' after
cts/tests/tests/dynamic_linker has been converted to Android.bp.

Change-Id: I93ec2aed3f3b185d320e56b1b4eebb71339b81ee