Improve IME perf test show/hide stability

Improve stability of perf tests for ImePerfTests:
1. testShowImeWarm
2. testHideIme

To improve the stability of the test, check IME state and if state is
not as expected, ignore the iteration rather than failing all the
iterations and hence the whole test.

Bug: 180449596
Test: Run the test using steps in Readme.md
Change-Id: Ie42cb49bd8f79af10e7fa48f0a3afb19f253476c