ewaol-tests: Move common test files to separate package

This patch brings the following changes:
 - Replaces 'sed' substitution calls with 'envsubst'.
 - Removes unused variable 'TEST_SUITE_PREFIX'.
 - Reworks '*-integration-tests.bb' recipes:
   * Moves common code to 'runtime-integration-tests.inc'.
   * Moves common runtime test files into a new package
     'runtime-integration-tests-common.bb'.
   * Allows to execute tests 'bats' files from any path.

Issue-Id: SCM-4421
Signed-off-by: Kamil Dziezyk <kamil.dziezyk@arm.com>
Change-Id: Ic2a251e7ba41e263ac7c5b0e705e7b910601df6a