Refactor test 1953, 1954, 1955, & 1956 somewhat

These tests all use a common set of suspension triggering event code.
This will be useful in other tests later. To make it easier to use in
the future this code is separated into common ti-agent files.

Test: ./test.py --host -j80
Change-Id: I75f3fe8862c99bd32c5eabe0992fef911d7d9c56
9 files changed