Allow chained startInstrumentation if it's originated from SHELL

If an instrumentation starts another instrumentation and so on,
and the original instrumentation is started from SHELL, allow all
Context#startInstrumentation calls in this chain.

Bug: 237766679
Test: atest CtsAppTestCases:InstrumentationTest
Change-Id: I3ea7aa27bd776fec546908a37f667f680da9c892